摘要:

Org. 23 Applications of High-potential Quinones. Part 1V.l The Mechanism of Oxidation of 6-Hydroxytetralins By J. W. A. Findlay and A. B. Turner," Department of Chemistry, University of Aberdeen, Aberdeen AB9 2UE Benzylic oxidation of 6-hydroxytetralins by 2.3-dichloro-5.6-dicyanobenzoquinone occurs readily in alcoholic solvents at room temperature. The corresponding 6-hydroxytetralin-I -ones are obtained by the use of two equiva- lents of the quinone, whereas with one equivalent the major products are 1 -alkoxy-derivatives. Isolation of the latter adducts provides evidence for the participation of quinone methides as intermediates in the oxidation process. The role of n-complexes in the initial hydrogen-transfer step is discussed. BECKER has established that methanolic dichlorodi- cyanobenzoquinone (DDQ) is a convenient reagent for the benzylic oxidation of p-cresols.2 Aldehyde formation is explained by successive nucleophilic attack of the solvent upon quinone methide intermediates formed by dehydrogenation. Here we describe studies on the oxidation of related bicyclic phenols, which were undertaken in order to investigate the behaviour of the quinone methide chromophore in a fused-ring system where tautomerisation may compete with ad- dition of a nucleophile.6-Hydroxytetralin (1) was readily oxidised by dichlorodicyanobenzoquinone at room temperature. The initial dark green solution soon became red-brown, and then pale orange in colour. When two equivalents of the quinone were employed, and the methanolic solution was kept under nitrogen for 2 h, a quantitative yield of hydroquinone was obtained and a single product was formed from the substrate phenol (1).It was isolated by t.1.c. and shown to be 6-hydroxytetralin- l-one (5). The formation of this ketone (isolated in 76% yield) is rationalised by a mechanism (Scheme 1) analogous to that proposed by Becker for the oxidation of 4-methyl-2,6-di-t-butylphenol to 4-hydroxy-3 5-di-t- butylbenzaldehyde. The yield of the tetralone (5) decreased when the oxidation was- carried out under oxygen, and traces of a second product were detected by t.1.c. The latter could not be isolated in amounts sufficient for complete characterisation, but the spectral data obtained suggest that it is a dimeric tetralone derivative. Reaction of 6-hydroxytetralin (1) with one mol.equiv. of dichlorodicyanobenzoquinone in the inert solvent dioxan did not yield the bicyclic quinone methide postulated in Scheme 1. Instead, a complex Part 111, J. W. A. Findlay and A. B. Turner, Org. Synth., 1969, 49, 53. 2 H.-D. Becker, J . Org. Chem., 1965, 30, 982 and 989. mixture of products was formed, probably arising from this species by tautomerisation and addition reactions. Since none of the intermediates postulated in Scheme 1 were detected in the reaction mixture, various ortho- substituted phenols were synthesised in the hope that Me0 OMe /HO\ m, / I \. n SCHEME 1 the introduction of bulky substituents such as t-butyl and iodo-groups would stabilise some of the inter- mediates involved. Reaction of 6-hydroxytetralin and isobutene in benzene solution containing conc.sulphuric acid as catalyst gave 6-hydroxy-7-t-butyl- tetralin (2) in moderate yield. In agreement with this structure, no coupling could be detected between the aromatic protons in the n.m.r. spectrum of the phenol (2), or in that of its monoacetate (see Table 1). No trace Turner, Chena. and Ind., 1970, 158. 81, 1176. Preliminary communication, J. W. A. Findlay and A. B. 4 C. D. Cook and B. E. Norcross, J . Amer. Chem. Soc., 1959,24 of the corresponding di-t-butylphenol was detected, even after prolonged heating in benzene. Steric con- gestion close to the ring junction is presumably re- sponsible. Attempts to introduce a second t-butyl group into the t-butylphenol (2) by treatment with TABLE 1 N.m.r. data for 6-hydroxytetralins Compound 6-Hydroxytetralin (1) 6-Hydroxy- 7- t-bu tyl- tetralin (2) 6-Hydroxy-5-iodo-7-t- butyltetralin (3) 6-Hydroxy-5 7-di-iodo- tetralin (4) 6-Acetoxy-7-t-butyl- tetralin 5,5’-Bis-( 6-hydroxy-7-t- butyltetralin) (12) 5,5’-Bis- (6-hydroxy- 7- t- butyltetralin) 6- acetate 6-Hydroxy-5,’I-di-iodo-l- methoxytetralin (10) 1 - Ethoxy-5,7-di-iodo-6- hydroxytetralin (11) 7 Values 8.26 (m, 4H) 7.33 (m, 4H) 4*66(br s, 1H) 2’84-3.56 (mJ 3H) 8.69 (s, 9H) 8.33 (m, 4H) 7.42 (m, 4H) 5.31(br s, 1H) 3.72 (s, 1H) 3.13 (s, 1H) 8.73 (s, 9H) 8.34 (m, 4H) 7.46 (m, 4H) 4-64 (s, 1H) 3-29 (s, 1H) 8-27 (m, 4H) 7.42 (m, 4H) 4.51 (s, 1H) 2.70 (s, IH) 8.68 (s, 9H) 8.24 (m, 4H) 7.70 (s, 3H) 7.20 (m, 4H) 3-32 (s, 1H) 2.97 (s, 1H) 8.61 (s, 18H) 8-28 (m, 8H) 7.85 (m, 4H) 7.25 (m, 4H) 5.13 (s, 2H) 2-94 (s, 2H) 8.66 (s, 9H) 8-62 (s, 9H) 8-29 (s, 3H) 5.07(br s, 1H) 3.03 (s, 1H) 2.86 (s, 1H) 8.17 (m, 4H) 7.36 (m, 2H) 6-59 (s, 3H) 5.84 (m, 1H) 4*14(br s.1H) 2.33 (s, 1H) 8-74 (t, J = 7Hz, 3H) 8.16 (m, 4H) 7-40 (m, 2H) 6-45 (t, J = 7Hz, 2H) 5-72 (m, 1H) 4.13 (s, 1H) 2.33 (s, 1H) Assignment C(2) and C(3), *CH,* C(l) and C(4), *CH,* C(6), OH C(5), C(7), and C(8), C(7), But C(2) and C(3), CH,. C( 1) and C(4), *CH,* c(6), OH C(5) , aromatic H C(8) , aromatic H C(7), But C(2) and C(3), CH,. C(l) and C(4), CHa* C(6), OH C(8) aromatic H C(2) and C(3), CH,* C(l) and C(4), CH,* C(6), OH C(8) , aromatic H C(7), But C(2) and C(3), CH,* C(6), OAc C(l) and C(4), *CH,* C( 8), aromatic H C(5), aromatic H C(5) and C(5‘), But aromatic H C(6), C(7), ‘C(6’), and C(1) and C(l’), CH,* C(4) and C(4’), CH2* C(6) and C(S‘), OH C(8) and C(8’), arom- C( 77, CH,.atic H C(6), But C(6), But C(6), OAc C(6’), OH C(8’), aromatic H C(8), aromatic H CH,* CH, C(1), OMe C(1), CH C(6), OH C(8), aromatic H *CH,*CH, CH, CH, -CH,*CH, C(1), CH c(6), OH C(8), aromatic H isobutene in the higher-boiling solvent toluene, resulted only in dealkylation to give the original tetralin (1). However, iodination of the phenol (2) with iodine and mercury(I1) acetate in acetic acid readily gave the iodo-t-butylphenol (3). Direct iodination of 6-hydroxy- tetralin (1) by the same method, with two mol. equiv. of iodine, gave the di-iodo derivative (4). The spectral J. Chem. SOC. (C), 1971 characteristics of these phenols, and of their oxidation products, were in accord with the assigned structurz (Tables 1 and 2).TABLE 2 N.m.r. data for substituted 6-hydroxytetralin-I-ones Compound T values 6-Hydroxy-7-t-butyl- 8.62 (s, 9H) tetralin-l-one (6) 7-88 (m, 2H) 7.43 (m, 2H) 7.21 (m, 2H) 3-39 (s, 1H) 3-33 (s, 1H) 1.98 (s, 1H) 6-Hydroxy-5-iodo-7-t- 8-62 (s, 9H) butyltetralin-l-one (7) 7-85 (4, 2H) 7.42 (t, 2H) 7.12 (t, 2H) 3.83 (s, 1H) 2.02 (s, 1H) 6-Hydroxy-5,7-di-iodo- 7-83 (m, 2H) tetralin-l-one (8) 7-46 (m, 2H) 7.08 (m, 2H) 3*72(br s, 1H) 2.60 (s, 1H) Assignment C(7), But C(3), CH,. C(4), CH,. C(2), *CH,* C(5), aromatic H C(6), OH C(8) , aromatic H C(7), But C(3), CH,* C(4), *CH,* C(2), *CH, (761, OH C(8) , aromatic H C( 3), CH,* C(4), CH,* C( 2), CH,* C(6), OH C(8), aromatic H Oxidation of these substituted 6-hydroxytetralins (2)-(4) under conditions similar to those used for the parent phenol gave good yields of the corresponding tetralin-l-ones (6)-(8) as the sole products.However, treatment of conc. methanolic solutions of the iodo- phenols (3) and (4) with one mol. equiv. of dichloro- dicyanobenzoquinone gave the corresponding l-methoxy- tetralins (9) and (10) as major products. Similarly, oxidation of the di-iodophenol (4) in ethanol gave the l-ethoxy-derivative (11). The base peaks in the mass spectra of these monoadducts correspond in each case to the loss of a molecule of alcohol from the molecular ion ; subsequent fragmentation involves loss of the C-5 and C-7 substituents, before final disintegration of the ring system. The characteristic loss of the mole- cule of alcohol probably leads directly to the correspond- ing styrene. under electron impact, rather than to the quinone methide, since only (M - RO) and (M - ROH) peaks are prominent in the mass spectra.No x FIGURE further loss of a hydrogen atom is consistent with the expected retention of the aromatic ring in these frag- ments (Scheme 2). An adduct was also obtained in good yield when the di-iodophenol (4) was oxidised with one mol. equiv. of quinone in n-butanol, but this proved to be particularly unstable and broke down to purple material 5 A. Hillmann-Elies, G. Hillmann, and V. Schiedt, 2. Natur- forsch., 1953, 8b, 436.Org. 25 during attempted purification by t.1.c. Complete characterisation of this material was not achieved. This group of products arises by 1,6-addition of alcohols to the quinone methide intermediates: and represents the half-way stage in the oxidation process depicted in Scheme 1. The reaction is useful, within strict structural limits, as a synthetic method for the benzylic alkoxylation of phenols.In view of the biological importance of benzylic hydroxylation in the catechol- amine series, we attempted to adapt the method to allow the introduction of a hydroxy-group. However, in spite of the ability of water to assume the role of r + m/e 398 SCHEME 2 methanol in the addition process, it was not possible to avoid further oxidation to the ketone stage (probably because this can now occur directly). 6-Hydroxytetra- lin (1) gave a product mixture consisting of roughly equal amounts of starting material and product tetra- lone (5), when treated with one mol.equiv. of the quin- one in aqueous dioxan. Thus final oxidation of the intermediate 1-hydroxy-compound to the ketone ap- pears to occur more rapidly than earlier steps in the sequence. This, in turn, is consistent with attack upon a tertiary rather than upon a secondary hydrogen atom, and with the known oxidation of ally1 and benzyl alcohols by dichlorodicyanobenzoquinone.7 Use of two mol. equiv. of the quinone in aqueous dioxan led to exclusive formation of the tetralones. Efficient benzylic hydroxylation probably cannot be achieved in this system, although the possibility cannot be ruled out until the rate-determining identified. HO step & the sequence is 0 A different type of product was also detected when the mono-t-butylphenol (2) was oxidised.This was of much higher RF value than the starting 6 A. B. Turner, Quart. Rev., 1964, 18, 347; Fortschr. Chem. oyg. Naturstofle, 1966, 24, 288. phenol, and, by the use of conc. solutions and 0.5 mol. equiv. of quinone, the yield of this material was increased to 45%, although some tetralone (6) was still formed. The i.r. spectrum of the new product showed no carbonyl absorption, but a sharp hydroxy- absorption was present at 3500 cm-l. Its U.V. spectrum resembled that of the starting phenol. The compound was relatively insoluble, and high resolution mass spectral analysis established that it was a dehydro- dimer of the starting phenol, having the molecular formula C,H,,O,. This leads to assignment of the 5,5’-bis-(6-hydroxy-7-t-butyltetralin) structure (12), as dirnerisation by phenolic coupling can only occur through the free ortlzo-position.Molecular models show that there is considerable steric hindrance to rotation about the new carbon-carbon bond in this compound, the planes of the two aromatic rings being mutually perpendicular in the preferred conformation. This explains the lack of conjugation between these rings (u.v. spectrum), and also the separation of the benzylic protons into two multiplets in the n.m.r. spectrum (Table 1). This is consistent with the changed environment of two of the benzylic methylene groups, which now lie above the plane of the opposite aromatic ring of the second monomer unit. The dimer could be acetylated only slowly with acetic anhydride, owing to the highly hindered nature of the hydroxy-groups.Furthermore, only a monoacetate was obtained, and this as an intractable gum. The resistance of the second hydroxy-group to acetylation is ascribed to hydrogen bonding with the carbonyl oxygen of the ester group first introduced, as this can occur without distortion in the preferred conformation of the molecule. The dimer (12) was not oxidised by potassium ferricyanide. The dimerisation of P-naphthols on treatment with inorganic oxidants is well known,8 and further oxidation to cyclic ethers is often observed. The failure of the dimer (12) to undergo further oxidation with this reagent is probably due to the twisted orientation of the coupled monomer units. The dimer was further attacked by dichlorodicyanobenzoquinone in methanol, but many products were formed and their isolation was not attempted. Oxidation of the t-butylphenol (2) with Fremy’s salt gave an unstable orange oil which, when studied immediately after isolation, appeared from its spectral data to be the ortho-quinone (13).The oil, even when kept under nitrogen, decomposed (detected by t.1.c.) after a few hours. The n.m.r. spectrum of a sample which was kept overnight in deuteriochloroform re- vealed two olefinic signals, z 3-58 (d, J = 7.5 Hz) and 3-50 (s), whereas the freshly-prepared solution showed only 7 3-50 (s). This evidence suggests that decomposi- tion of the ortho-quinone (13) occurs via the tautomeric hydroxyquinone methide (14). Hydroxy-group ab- sorption was present in the n.m.r.and i.r. spectra. No 7 D. Walker and J. D. Hiebert, Chem. Rev., 1967, 67, 153. 8 R. Pummerer and F. Frankfurter, Ber., 1914, 47, 1472; R. Pummerer. E. Prell, and A. Rieche, ibid., 1926, 59, 2169.26 J. Chem. SOC. (C), 1971 satisfactory quinoxaline derivative could be formed from the original quinone, and further characterisation of the material was not achieved. 6-Methoxytetralin (15) was also readily oxidised to 6-methoxytetralin-l-one (16) (70% yield) by two mol. equiv. of dichlorodicyanobenzoquinone in methanol. Here, participation of a discrete quinone methide is clearly impossible, but abstraction of hydride ion from the benzylic position is assisted by delocalisation of charge in the resulting cation (17). Nucleophilic ad- dition of the alcohol is apparently unimpaired.How- ever, the presence of a strongly electron-releasing group para to a benzylic position is necessary, as no a-tetralone was detected when tetralin itself was subjected to the same conditions. The tetralone (16) is an important starting material for the total synthesis of steroids by the vinylcyclohexanol route. Although it can be prepared from the tetralin (15) by chromium(II1) trioxide oxidation, there has been recent interest in the development of methods of aerial oxidation with homogeneous cataly~is.~ This work provides an altema- tive reagent for achieving the oxidation in homo- geneous solution. Some general comments may be made regarding the mechanism of these quinone oxidations. Direct evidence for the role of solvent in the proposed scheme is provided by isolation of the intermediate monoadducts (9)-(11), with further support from the similarity of the yields of tetralones obtained by the use of ethanol or aqueous dioxan instead of methanol.No intermediates between the monoadducts and the product tetralones were detected. Acetals may be formed (cf. ref. 2), but in our reactions enol ethers could also be involved, or the tetralones may arise by direct cleavage of the quinone methides formed in the second dehydrogenation step (See Scheme 1). Solvent participation in turn provides evidence for the involvement of quinone methides in the oxidation process, but again these intermediates were not isolable, even when blocking groups were present in the ortho- positions. The isolation of stable quinone methides as end products of related oxidations has been reported recently.l* Also, the initial quinone methides clearly suffer nucleophilic attack by the alcohol, in preference to tautomerisation to the corresponding styrenes, in the presence of a large excess of the alcohol.This is in contrast with the behaviour of fully substituted quinone methides generated under similar conditions from steroidal phenols.ll Here tautomerisation to styrenes is observed, probably due to steric effects. There remains to be discussed the precise mechanism of the initial hydrogen-transf er process leading to form- ation of the quinone methides. Although the bulk of previous work favours a free-radical mechanism, the oxidation could also proceed by removal of hydride ion from the activated benzylic position.The isolation A. J. Birch and G. S. R. Subba Rao, Tekahedron Letters, 1968, 2917; cf. ref. 19. lo H.-D. Becker, J. Org. Chem., 1969, 34, 1203. of the coupled dimer (12) in concentrated solution supports earlier conclusions regarding the participation of phenoxy-radicals in this type of redox system, and the same dimer is obtained from the phenol (2) (9) R ' = E ~ , R*=M~ 2 (11) R'=I, R*=E~ (12) (10) d= I , R =Me 0 (13) X & Me0 (15) X=H, (16) X = 0 Bur (18) by the use of recognised one-electron oxidants such as alkaline potassium ferricyanide, neutral iron(m) chloride, and activated manganese dioxide (quantitative yield). The difference in oxidation potential between chloranil and dichlorodicyanobenzoquinone was emphasised by the failure of chloranil to produce tetralones from these tetralins in methanol, even at reflux temperature, although chloranil has recently been found to oxidise 2,4-di-t-butylphenol to the dimer (18) .12 This suggests that the key factor in the formation of tetralones with the higher-potential quinone lies in its ability to achieve further oxidation of the phenoxy-radical, perhaps by abstraction of hydrogen from the benzylic carbon atom.The ease of oxidation of the hindered phenols (3) and (a), and particularly of the methyl ether (15), also indicates that attack by dichlorodi- cyanobenzoquinone is mounted at the benzylic carbon atom. Thus, abstraction of hydride ion is a possible 11 W. Brown, J. W. A. Findlay, and A. B. Turner, Chem. l2 H.-D. Becker, J. Org.Chem., 1969, 34, 1198. Comm., 1968, 10.Org. 27 first step, in common with the initial action of this oxidising agent upon many other substrates.13 The dark colours produced in the early stages of these reactions prompt the consideration of concerted mechanisms occurring after formation of x-complexes (cj. Figure). Models indicate that one of the para- benzylic C-H bonds in the tetralin molecule is virtually perpendicular to the plane of the aromatic ring, and hence is favourably disposed for the maintenance of Q--x overlap during hydride ab~tracti0n.l~ In agreement with electron transfer within a x-complex, the colours fade rapidly as oxidation proceeds. In the case of the dimeric phenol (12) there is no deep colouration upon treatment with dichlorodicyanobenzoquinone, and no single oxidation product predominates.Restricted rotation of the monomer units precludes efficient x-complex formation with the quinone. EXPERIMENTAL 1.r. and U.V. spectra were determined with Perkin- Elmer 237 and 137 spectrophotometers, respectively. N.m.r. spectra were recorded with a Varian A-60 instru- ment for solutions in deuteriochloroform, with tetra- methylsilane as internal reference, and mass spectra with an A.E.I. spectrometer Model MS-902. For general directions see Part II.15 6-Hydroxytetralin was prepared by the literature method,16 b.p. 115-120' at 2-3 mmHg (1it.,l6 121- 124' at 2.5 mmHg), m.p. 53-55" (1it.,l6 58-59"). 6-Meth- oxytetralin was obtained by the literature method l7 in 66% yield, h.p. 8 6 8 6 ' at 2.5-3-0 mmHg (lit.,17 134- 138" at 18 mmHg).6-Hydroxy-7-t-butyZtetralin (2) .-Isobutene was bubbled through 6-hydroxytetralin (1.5 g) in benzene (5-0 ml) and conc. sulphuric acid (0.1 ml) at 60-70' until less than 5% of starting material remained (t.1.c.). Benzene (20 ml) was added, and the organic layer was washed with 2 ~ - sodium hydroxide followed by water, and dried (MgSO,). Evaporation of the solvent left a brown oil (1.77 g, 86%). Distillation gave the phenol as a viscous oil, b.p. 115- 125' at 3.0 mmHg, which crystallised slowly, m.p. 54- 56" [Found: C, 81.5; H, 9.8%; M (mass spectrum), 204.1514. C1,H2,0 requires C, 82.3; H, 9.8%; M , 204.15141, vmax 3520 and 1620 cm-1, Amx. 282.5 nm (E 4270). 6-A cetoxy- 7-t-Buty2tetvaZin.- 6-Hydroxy-7-t-butyltetralin (200 mg) in pyridine (5.0 ml) was treated with acetic anhydride (1.0 ml) at room temperature.Next day the solution was diluted with water, and extracted with chloro- form. The organic layer was washed successively with dilute hydrochloric acid, aqueous sodium hydrogen- carbonate, and water, and dried. Removal of the solvent gave 6-acetoxy-7-t-butyZtetralin as a pale yellow oil (205 mg) . An analytical sample was obtained after two short-path distillations; b.p. 105-1 10" a t 0.1-0.15 mmHg (Found: C, 78.1; H, 9.2. CI6H2,O2 requires C, 78.05; H, 8-9%), hma, 277 nm (E 3980). l3 L. M. Jackman, Adv. Org. Chem., 1960, 2, 329; A. B. Turner and H. J. Ringold, J . Chem. SOC. (C), 1967, 1720; cf. J. W. A. Findlay, P. Gupta, and J. R. Lewis, ibid., 1969, 2761. l4 Cf. W. Brown, A. B. Turner, and A.S. Wood, Chem. Comm., 1969, 876. A. B. Turner, J . Chem. SOG. (C), 1968, 2568. Attempted A ZkyZation of 6-Hydroxy-7-t-butyZtetraZin.- Isobutene was bubbled through a refluxing solution of the mono-t-butylphenol (800 mg) in toluene (4.8 ml) and conc. sulphuric acid (0-06 ml.) for 18 h. The mixture was pro- cessed as before to give a gum, which was shown by t.1.c. [benzene-hexane (1 : l)] to consist of starting material and a compound of RF value identical with that of 6-hydr- oxytetralin, in approximate ratio 2 : 3 (by iodine vapour location). A sample of the less mobile compound isolated by preparative t.1.c. was identical with 6-hydroxytetralin. 6-Hydroxy-5-iodo-7-t-butyltetraZin.-(a) B y iodination in the presence of PPzercury(11) acetatee5 6-Hydroxy-7-t-butyl- tetralin (200 mg) in acetic acid (5 ml) was added to mer- cury(I1) acetate (170 mg) in acetic acid (10 ml).After stirring for 10 min, a saturated solution of iodine (270 mg) in acetic acid was added, with stirring, during 5 min a t 60-70'. Stirring was continued for 3 h at 60-70", and the precipitated mercury(I1) iodide was filtered off. The filtrate was reduced to a quarter volume in vacuo and diluted with water. Extraction with ether, and successive washing of the organic extracts with 40% aqueous sodium hydrogen carbonate solution, aqueous potassium iodide, and water, followed by evaporation of the dried ethereal solution, gave an orange gum (235 mg) which was chromatographed on a silica gel column. Elution with benzene-hexane (1 : 4) gave 6-hydroxy- 5-iodo-7-t-butyltetvalin (122 mg; 38%), m.p.62-64' (Found: M , 330.0476. C,,H,,IO requires M , 330.0483), A,, 281 nm (E 5050). Further elution with hexane- benzene mixtures up to 100 yo benzene gave starting material (87 mg) . 6-Hydr- oxy-7-t-butyltetralin (90 mg) was applied in chloroform to three 20 x 20 cm silica gel t.1.c. plates, which were then developed in benzene-hexane (1 : 4). The plates were exposed to iodine vapour for 12 h, and excess of iodine was removed by gentle warming. The brown band was eluted with chloroform, and the eluate was washed with aqueous potassium iodide, followed by water, and dried. Removal of solvent left a purple gum, which was re- chromatographed to give starting material and 6-hydroxy- 5-iodo-7-t-butyltetralin (62 mg) as an oil, identical (ix.spectrum and B, value) with material prepared by method 6-Hydvoxy-5,7-di-iodotetraZin.-6-Hydroxytetralin (0.60 g) in acetic acid (7.5 ml) was added to mercury(I1) acetate (1.28 g) in acetic acid (60 ml) at 60-70'. After stirring for 10 min, a saturated solution of iodine (2.08 g, 2 mol. equiv.) was added dropwise during 5-10 min. Stirring was continued a t this temperature for 3.5 h and the mix- ture was worked up as before. The crude product (0.59 g of black tar) was chromatographed on silica gel. Elution with benzene-hexane (1 : 4) gave a colourless oil (0.55 g) which was further purified by t.1.c. with the same solvent system. Final percolation , in chloroform solution, through a column of acid-washed Celite 545, followed by evaporation, left 6-hyd~oxy-5,7-di-iodotetralin as an oil which crystallised to give prisms, m.p.47-48" (Found: C, 30.4; H, 2.4. C1,H1,120 requires C, 30-0; €3, 2.5%), Am=. 287 nm (E 4000). 179. Chem. SOC., 1940, 727. (b) B y iodination on silica gel chromatograms.18 (4- l6 S. Goodwin and B. Witkop, J . Amer. Chem. SOC., 1957, 79, l7 V. C . E. Burnhop, G. H. Elliott, and R. P. Linstead, J . l8 W. Brown and A. B. Turner, J . Chromatog., 1967, 26, 518.28 Oxidation of 6-Hydvoxytetralin by Two Equivalents of Dich1orodicydnobenzoquinone.-(a) In methanol under an inert atmos9heve. The quinone (184 mg) was added to a deoxygenated solution of the phenol (60 mg) in methanol (2 ml), under an atmosphere of nitrogen. The initial deep green colour decayed rapidly to a red-brown and finally to pale orange.After 2 h at room temperature, the methanol was removed under reduced pressure, and the residue was extracted with warm benzene. The insoluble hydroquinone (180 mg) was filtered off, the filtrate was evaporated; and the residue was separated by t.1.c. (benzene-ethyl acetate, 3 : 1) into unchanged starting material (4 mg) and 6-hydroxytetralin-1-one (50 mg; 76y0), m.p. 149-150°, identical (i.r. spectrum, m.p., and mixed m.p.) with an authentic sample. No other products were detected by t.1.c. (b) I n ethanol. Oxidation as in (a) with ethanol as solvent gave 6-hydroxytetralin-1-one (48 mg, 73%) as the sole product. The oxidation was repeated with the phenol (100 mg) and the quinone (307 mg) in methanol (3 ml) in the presence of atmospheric oxygen.Work-up as in (a) gave starting phenol (16 mg), 6-hydroxy- tetralin-1-one (78 mg), and a product of intermediate B p value as an oil (4-9 mg) (Found: M , 320.1420. C,lH,OO, requires M , 320*1412), 1,- 225.5 (E 33,330), 250s (17,870), 275 (16,530), and 335s nm (1870), v- (film) 3350, 1690, 1600, and 1570 cm-l. (d) I n anhydrous dioxan. A solution of the phenol (100 mg) in anhydrous dioxan (3 ml) was treated with the quinone (169 mg; 1.1 mol. equiv.). Hydroquinone pre- cipitated from the resulting deep green solution after 3 min. Examination of the filtrate by t.1.c. after 1 h revealed a complex mixture of products, which was not further investigated. (e) I n aqueous dioxan. Dichlorodicyanobenzoquinone (61 mg) in dioxan (3.0 ml) was added dropwise during 15 min to 6-hydroxytetralin (40 mg) in dioxan (1.0 ml) and water (0.25 ml). After each drop the solution was allowed to decolourise before the next addition. The final pale orange solution was left for 3 h at room temper- ature before the precipitated hydroquinone (45 mg) was filtered off and the filtrate was evaporated.T.1.c. of the residue (ethyl acetate-toluene, 1 : 4) gave starting material ( 14 mg) and 6-hydroxytetralin- 1-one ( 15 mg) . 6-Hydroxy-5,7-di-iodotetralin-l-one (8) .-6-Hydroxy-5,7- di-iodotetralin (100 mg) in methanol (3.0 ml) was treated with dichlorodicyanobenzoquinone (1 14 mg, 2 mol. equiv.) and the solution was left at room temperature for 2 h. Similar colour changes to those in the oxidation of 6-hydr- oxytetralin were observed. One main band was obtained upon t.1.c.of the crude product. This was eluted with ethyl acetate ; evaporation afforded the di-iodotetralone, prisms (84 mg, 78y0), m.p. 153-155" (from chloroform- methanol) (Found: C, 28.7; H, 2.1. ClOH,I2O2 requires C, 29.0; H, 1.9%), 240 and 275 nm (E 25,172 and 11,290), v- (Nujol) 3230, 1668, and 1555 cm-1. This product was also obtained in aqueous dioxan. The quinone (70 mg) was added to the phenol (50 mg) in 2% aqueous dioxan (2.5 ml) and the resulting deep brown mixture was left overnight at room temperature. After removal of hydroquinone (67 mg), B-hydroxy-5,7-di-iodotetralin- 1-one (44 mg; 82%), m.p. 147-153", was isolated as the sole product by t.1.c. 6-Hydroxy-5-iodo-7-butyZtetralin- 1-one (7) .-6-Hydroxy- (c) I n methanol in air. J. Chem.SOC. (C), 1971 5-iodo-7-t-butyltetralin (50 ing) in methanol (1.5 ml) was treated with dichlorodicyanobenzoquinone (70 mg ; 2 mol. equiv.) during 1 h at room temperature. Preparative layer chromatography penzene-hexane (4 : l ) ] gave the tetralone (36 mg; 65%), prisms, m.p. 113-114.5' (from aqueous methanol, (Found: C, 48-2; H, 5.2. C14Hl,I0, requires C, 48.8; H, 4.9), & 235 and 283-5 nm (E 19,400 and 10,920), v,, (Nujol) 3340, 1658, and 1580 cm-1. Oxidation of 6-Hydroxy-'I-t-butyltetralin.-(a) With 2 mol. equiv. of quinone. The phenol (50 mg) in methanol (1.5 ml) was oxidised as before with the quinone (88 mg) overnight. The usual work-up gave 6-hydroxy-7-t-butyltetruZin- 1-one as a solid (32 mg, 60%), m.p. 225-227" (decomp.) (Found: M , 21801310. Cl,H1802 requires M , 218.1307), &= 230 and 282.5 nm (E 18,800 and 10,350), v,, (Nujol) 3300, 1665, and 1595 cm-l.(b) With 0.5 wzol. equiv. of quinone in concentrated solzction. The phenol (200 mg) in methanol (1.0 ml) was treated with dichlorodicyanobenzoquinone (88 mg ; 0.5 mol. equiv.} . The deep colour formed on mixing dispersed rapidly and a solid precipitated. The mixture was left overnight before the precipitate was collected (66 mg). T.1.c. of the mother liquors furnished more of the same material (14 mg), together with traces of 6-hydroxy-7-t-butyltetralin-1-one. Recrystallisation of the main product from methanol gave 5,5'-bis-( 6-hydroxy-7-t-bwtyltetralin) as needles, m.p. 184- 185" (Found: C, 81.9; H, 9.4; M , 406.2861. C28H3803 requires C, 82.7; H, 9.4%; M , 406-2872), A- 268.5 nm (E 3570), v- (Nujol) 3500, 1610, and 1580 cm-l.The dimer (100 mg) was acetylated in pyridine (2.5 ml) with acetic anhydride (0.5 ml) by heating on a steam-bath for 2-5 h. Dilution with water, followed by chloroform extraction, gave a gum (105 me) which was separated by t.1.c. into starting material (30 mg) and the much less mobile 5,5'-bis-( 6-hydroxy-7-t-butyltetralin) 6'-acetate, iso- lated with chloroform as a gum (65 mg) which could not be crystallised (Found : M , 448.2987. C30H,o0, requires M , 448.2977), I.,, 278.5 nm (c 7280), v,, 3500 and 1750 cm-l. The n.m.r. spectrum (Table 1) confirmed the mono- acetate structure. 6-Hydroxy-5-iodo- 1-methoxy-7-buty ZtetraZin (9) .-6-Hydr- oxy-5-iodo-7-t-butyltetralin (100 mg) in methanol (1.0 ml) was treated with the quinone (70 mg, 1 mol.equiv.). After 3 h. at room temperature, separation of the crude mixture by t.1.c. [benzene-hexane (1 : l)] gave traces of starting material, the tetralone (23 mg), and the 1-methoxy- tetralin as a colourless gum (60 mg, 55%) (Found: M , 360.0588. Cl,H,lIO, requires M , 360.0589), A,, 279 and 286 nm (c 2600), vmx. 3445 and 1595 cm-l. 6-Hydroxy-5,7-di-iodo-l-upzethoxytetvalin (10) .-5,7-Di- iodo-6-hydroxytetralin (50 mg) and the quinone (28 mg; 1 mol. equiv.) in methanol (0.5 ml) similarly gave the tetra- lone (12 mg), traces of starting phenol, and the 1-metkoxy- tetraZia as a buff solid (28 mg; 52y0), m.p. 147-148" (Found: M , 429.8927. C1,H1,120, requires M , 429*8930), &, 285 and 244s nm (c 4300 and 3520), vmK (Nujol) 3400 and 1610 cm-1; m/e 430 (M+), 399, 398 (base peak, M - CH,OH), 272, 271, 145, 144, and 115. l-Ethoxy-6-hydroxy-5,7-di-iodotetrulin (1 1) .-The fore- going reaction was repeated, with ethanol instead of meth- anol, to give the I-ethoxytetralin (54%) as buff crystals, m.p.144-145O (Found: M , 443.9078. C13H1,1,02 re- quires M , 443.9088), & 285 and 295s nm (E 3070 and 2900), v- (Nujol) 3440 and 1570 cm-l; m/e 444 (Mf), 399, 398 (base peak, M - C,H,OH), 272, 271, 145, 144,Org. 29 and 115. Starting phenol (14%) and the di-iodotetralone (22%) were also isolated. 6-MetlzoxytetraEin-1-one (1 6 ) .-Oxidation of 6-methoxy- tetralin (30 mg) in methanol (1.5 ml) with dichlorodicyano- benzoquinone (84 mg) , followed by t.1.c. separation [benz- ene-ethyl acetate, (12 : l)], gave 6-methoxytetralin-l-one (23 mg, 70%), m.p.77-78' (Lit.,lg 78') identical with an authentic sample. A €tempted Oxidation of Tetralin.-Tetralin (50 mg) and dichlorodicyanobenzoquinone ( 17 1 mg) in methanol (3-5 ml) were kept at room temperature for 18 h under nitrogen. The methanol was evaporated off and the product was isolated with benzene. Unchanged quinone was removed by percolation of a solution in ethyl acetate through a short column of neutral alumina.l5 Final evaporation left a pale yellow oil (30 mg) which showed no i.r. carbonyl absorption. Oxidation of 6-Hydroxy-7-t-butyltetralin with Inorganic Oxidants.-(a) Manganese dioxidtx2o A solution of the phenol (100 mg) in chloroform (25 ml) was stirred with active manganese dioxide (2.0 g) overnight. The solid was filtered off and the filtrate was evaporated in vacuo to leave a pale yellow gum. T.1.c. [hexane-benzene, (9 : l)] gave one main band, which was eluted with chloro- form to give 5,5'-bis-(6-hydroxy-7-t-butyltetralin) as a colourless solid (96 mg), m.p. 185-186', identical (mixed m.p. and i.r. spectrum) with the sample prepzred before. (b) Alkaline putassiuwz ferricyanide. To the phenol fl00 mg) in 4~-sodium hydroxide (10 ml) was added a solution of potassium ferricyanide (329 nig) . A precipitate formed immediately. The mixture was stirred for 2 h, acidified, and extracted with ethyl acetate. The organic layer was washed with saturated sodium hydrogen carb- onate solution, followed by water, dried, and evaporated to leave a gum which was separated by t.1.c. into unchanged phenol (68 mg) and 5,5'-bis-( 6-hydroxy-7-t-butyltetralin) Treatment of the phenol (100 mg) in ethanol (20 ml) with iron(II1) chloride (320 mg) in ethanol (12 ml) for 26 h, followed by a similar work-up, gave starting phenol (82 mg) and the dimer (6 mg). (25 mg). (c) Iron(m) chloride. We thank the S.R.C. for a research studentship (to [0/781 Received, May 12th, 19701 19 S. N. Ananchenko, V. Ye. Linanov, V. N. Leonov, V. N. 20 R. M. Evans, Quart. Rev., 1959, 18, 61. J. W. A. F.). Rzheznikov, and I. V. Torgov, Tetrahedron, 1962, 18, 1365.

ISSN:0022-4952    

DOI:10.1039/J39710000023

出版商:RSC    

年代:1971

数据来源: RSC