摘要:
1977 217Carbon-I 3 Nuclear Magnetic Resonance Spectroscopy of 1 -Tetralols andChroman-4-01sBy Yasuhisa Senda,' Jun-ichi Ishiyama, and Shin Imaizumi, Department of Applied Science, Tohoku Univer-sity, Sendai, JapanKaoru Hanaya, Department of Chemistry, Yamagata University, Yamagata, Japan13C N.m.r. spectra of 1 -tetralol, chroman-4-01. and their substituted homologues have been determined. TheCH (OH) resonances of 1 -tetra101 and chroman-4-01 indicate that their hydroxy-groups prefer a pseudoaxialorientation, as a result of strain. 13C N.m.r. spectra of stereoisomeric flavanols support the configurationalrelationship reported by Clark-Lewis eta/. and by others that the a-isomer corresponds to the cis- and the p-isomerto the trans-form.SUFFICIENT evidence has been accumulated to establishthat carbon shieldings depend, at least in part, onmolecular geometry and c~nformation.l-~ We havestudied the 13C n.m.r.spectra of a range of l-tetralolsand chroman-4-o1sJ primarily to ascertain the influenceof structure and stereochemistry on carbon chemicalshifts.RESULTS AND DISCUSSIONThe natural-abundance 25.15 MHz l3C Fourier trans-form n.m.r. spectra were obtained by using the IH noisedecoupling technique. 1H Off-resonance decouplingwas used to aid assignments of resonances to specificcarbon atoms. The chemical shifts obtained are listedin Table 1. The assignments of CH(0H) signals of1-tetralols are straightforward. The CH(0H) reson-ances of cis-3-methyl- (3) and cis-3-phenyl-l-tetralol (4)appear at lower field than those of their trans-counter-parts.The CH(0H) chemical shifts of 2-methylcyclo-hex-2-en01 (lo), and cis- and trans-2-methyl-5-t-butyl-cyclohex-2-enols (11) are 6 68.87, 71.53, and 68.80,re~pectively.~ As in the case of the 2-methylcyclohex-2-enols the C-1 resonance of l-tetralol (1) appearscloser to those of trans- (3) and trans- (4) than to those oftheir cis-counterparts. It has been reported that thehydroxy-group of the cyclohexenol(10) prefers a pseudo-axial orientation as a result of strain between thehydroxy-group at the allylic position and the methylgroup at the vicinal sfi2 hybridised carbon atom [A(1s2)strain 51. The magnitude of the interaction is estimatedas ca. 1.95 kcal mol-l.6 The equatorial methyl groupof Pmethylcyclohexene hardly affects the chemical shiftof C-6.' An equatorial phenyl group at C-4 is alsoexpected not to affect appreciably the chemical shift ofC-6 in cyclohexene.The correlation of the chemicalshift for C-1 of the tetralol (1) with that of the cyclo-hexenol (10) suggests that (1) exists in a conformationwith the hydroxy-group in a preferred pseudoaxial1 G. C. Levy and G. L. Nelson, ' Carbon-13 Nuclear MagneticResonance for Organic Chemists,' Wiley-Interscience, New York,1972.J. B. Stothers, ' Carbon-13 NMR Spectroscopy,' AcademicPress, New York, 1972.N. K. Wilson and J . B. Stothers, Topics Steveochem., 1974,8, 1.Y. Senda, S. Imaizumi, S. Ochiai, and K. Fujita, Teira-hedron, 1974, 80, 639.F. Johnson and S.K. Malhotra, J . Amer. Chem. SOC., 1965,87, 6492.orientation, as also indicated by an i.r. study.* LargeA(192) strain may also exist between the hydroxy-groupand the aromatic methine group at position 8. Whencis- (3) is in a conformation with the hydroxy-group ina pseudoaxial orientation, there is a large 1,3-syn-axial-pseudoaxial interaction between the methyl and thehydroxy-group. The energy of this interaction isestimated as ca. 2.2-2.4 kcal mol-l, the energy of the1,3-syn-diaxial interaction on a cyclohexane ring,g or.less. By comparing the A(1,2) strain of the hydroxy-group and the lJ3-syn-axial-pseudoaxial interactionbetween a methyl and a hydroxy-group on a cyclo-hexene ring, cis- (3) is deduced to be stabilised in aconformation with the substituents in an equatorialand a pseudoequatorial orientation by 0 .3 4 . 4 kcalmol-1 or less. This indicates that, even when A(192)strain is large, the hydroxy-group of cis- (3) prefers apseudoequatorial orientation. The C-3 resonances forthe tetralols (3) and (4) are easily assigned by use of theoff-resonance technique. If it is possible to apply thesubstituent parameters of a methyl group and a hydroxy-group on a cyclohexane ring to the saturated carbonatoms of a cyclohexene ring, other two resonances forthe alicyclic carbon atoms can be assigned appropriatelyto C-2 and -4. The resonances for C-2, -3, and -4 ofthe cis-isomers appear at lower field than those of thetram-forms as in the case of C-1.The C-2 resonances of chroman-4-ols are expected toappear close to the CH(0H) signals.The CH(0H)resonances of chroman-4-01 (5) and 4-rnethylchroman-4-01 (6) appear a few p.p.m. to higher field than those ofthe corresponding 1-tetralols because these carbonatoms are y with respect to the ethereal oxygen.lo Onthe basis of the substituent effect of the ethereal oxygen,the resonances of the stereoisomeric 2-methylchroman-4-01s (8) and flavan-Pols (9) which appear a few p.p.m.to higher field than those of the corresponding 1-tetralols, may correspond to c4. In comparing theY . Senda and S. Imaizumi, Tetrahedron, 1974, 80, 3813.T. Pehk, S. Rang, 0. Eisen, and E. Lippmaa, Eesti N.S. V .Tead. Akad. Toim. Keem. Geol., 1968, 17, 296.ti H. Iwamura and K. Hanaya, Bull.Chem. SOC. Japan, 1970,43, 3901.E. L. Eliel, ' Stereochemistry of Carbon Compounds,'McGraw-Hill, New York, 1962, p. 237.lo E. L. Eiel, W. F. Bailey, L. D. Kopp, R. L. Willer, D. M.Grant, R. Bertrand, K. A. Christensen, D. K. Dalling, M. W.Duch, E. Wenkert, F. M. Scheli, and D. W. Cochran, J . Amev.Chem. SOC., 1975, 97, 322218 J.C.S. Perkin ITABLE 113C Chemical shifts (6) of 1-tetralols and chroman-4-01sc-1 c-2 c-3 c-4 C-5 G 6 C-7 G 8 C-8a C-4a C-1' C-2',-6' C-3',-5' C-4' CH,67.70 32.15 18.99 29.18 (128.68) (125.89) (127.16) (128.68) 138.87 136.87No.(1)70.43 39.61 20.44 29.91 (126.92) (126.19) (126.43) (128.62) 143.00 136.08 30.7622.08 69.40 42.04 28.27 38.28 (126.86) (126.95) (126.86) (128.26) 139.60 136.50 cis- (3)67.95 39.92 23.66 38.10 (128.98) (126.19) (127.77) (129.65) 137.78 137.17 21.84 #taus-(3)OH69.89 40.34 39.31 38.28 (126.37) (126.85) (127.20) (128.44) 139.28 136.17 145.39 (126.71) 128.56 (126.37) cis- (4)67.76 38.58 34.70 37.61 (126.72) (127.94) (128.95) (129.79) 137.28 136.74 145.79 127.00 128.47 (126.37) traus-(4)61.88 30.82 62.91 129.77 120.43 129.47 116.91 154.46 124.3163.21 37.98 66.19 128.98 120.67 126.55 117.03 153.80 128.50 29.4260.61 30.94 60.00 136.02 121.46 130.07 121.22 162.83 123.6471.22 39.65 65.28 128.86 120.49 127.04 116.36 154.52 125.7715.8317.8921.41(7)cis- (8)21.17 67.34 37.67 63.64 130.20 120.37 129.71 117.15 155.07 123.68 trans-(8)76.94 40.17 65.89 (128.70) 121.01 (128.26) 116.80 164.54 126.11 140.66 127.03 129.20 (125.80) a- (9)73.04 38.22 63.76 (129.95) 120.79 (129.10) 117.45 164.83 125.77 140.93 126.19 128.56 (128.01)OHLMe -Q: 68.87 32.04 17.88 25.19OHcis- (11) 71.53 34.95 43.68 27.12MeMe 68.80 33.13 37.66 27.30Values in parentheses may be interchanged.O1977 219CH(0H) chemical shifts of the stereoisomeric alcohols(8) and (9) with those for (5), a similar correlation tothat with the l-tetralols is observed. This indicatesthat the hydroxy-groups of (5), trans- (8). and @- (9) alsoprefer the pseudoaxial orientation,ll while those ofcis- (8) and a- (9) prefer the pseudoequatorial position.The resonances for C-2, -3, and -4 of the cis-isomersappear at lower field than those of the trans-forms.The stereochemistry of the flavanols (9) has beendiscussed extensively.Clark-Lewis et aZ.12 and otherauthors13 have studied the lH n.m.r. spectra anddeduced from coupling constants that a- (9) correspondsto the cis- and @- (9) to the trans-isomer. The 13C n.m.r.spectra of these compounds support this configurationalrelationship. The CH(0H) resonance of (7) appears athigher field than that of parent chromanol. This maybe due to an increasing population of the conformerwith the pseudoaxial hydroxy-group owing to the largehydroxy-methyl strain at the allylic and the 9eripositions and/or the steric compression shift caused bythe methyl group at C-5.14J5The 13C n.m.r. spectra of the stereoisomeric l-t-butyl-4-methylcyclohexanes show that the chemical shift of anaxial methyl group in a cyclohexane ring is 6 17.53, andthat of an equatorial methyl group is 22.53.16 If thesevalues are applied to the methyl group at the homo-allylic position on a cyclohexene ring, the observedcarbon chemical shifts for the 3-methyl group of thestereoisomeric tetralols (3) indicate that these groupsprefer an equatorial orientation.In comparing thecarbon chemical shifts of cyclohexane and cyclohexenewith those of tetrahydropyran and dihydroyyran,respectively, no substituent effect on the @-carbon atomof l-tetralols and chroman-4-01s are easily assigned onthe following basis. (i) For comparisons of the chemicalshifts of the respective carbon atoms of allylic alcohols l7with those of the corresponding alkenes la with the samenumber of carbons, the substituent parameters of thehydroxy-group on both p- and y-carbon atoms arepositive,* the former being larger than the latter.In1-tetralols, the resonances for C-4a may appear at higherfield than those for C-8a. (ii) The resonances for sub-stituted carbon atoms of monoalkylbenzenes appeararound 6 140-150.19 The resonances around 6 145 in(4) and those around 6 140 in (9) correspond to C-1'.The chemical shifts for the aromatic carbon atoms inphenyl ethers such as anisole are usually in the order,substituted > meta- > para- > ortho-positions, since theelectronic effect of the oxygen atom produces an upfieldshift of ortho- and para-carbon signals, the formerappearing at higher field than the latter. The reson-ances around 6 116-117 in chroman-4-01s may corre-spond to C-8 and those around 6 120-121 to C-6.Ithas been reported that for toluene, the substituent ofwhich is relatively small, the resonances of the ortko-carbon atoms appear at a field lower than those for themeta-carbon atoms, whereas an inverse tendency due tosteric compression is found in monoalkylbenzenes whichhave a relatively large substituent such as a cyclohexylor an isopropyl g r 0 ~ p . l ~ In the phenyl-substitutedcompounds such as (4) and (9), the resonances for C-2'and C-6' or C-3' and C-5' are expected to appear at thesame position, those of the former two carbon atomsappearing at slightly higher field than those of the lattertwo. The signal intensity identifies these resonances.Other aromatic carbon signals are impossible to assignby replacement of a methylene with an oxygen atom wasobserved (Table 2).Therefore, the carbon chemicalto the specific nuclei.TABLE 2 EXPERIMENTALComparison of 13C chemical shifts of six-membered ringcompoundsN.m.r. S f i e ~ t r a . - ~ ~ C Fourier transform n.m.r. spectrawere obtained a t 25.15 MHz with a JEOL JNM-MH-100instrument equipped with a JNM-MFT- 100 Fourier trans-form accessory; the instrument was controlled with aJEC-6 spectrum computer. Samples were dissolved intoCDCl,, the deuterium signal of which provided a fieldfrequency lock; the concentrations were 20% (w/v).Measurement conditions were as follows; pulse width27.5 ps (ca. 45 "C); repetition time 4 s; spectral width6.25.kHz; data points 8 192. Noise modulated protondecoupling was carried out at a nominal power of 20 W.b 0, 21.42 b 6, 26.070, % 0% 23.058 23.11All chemical shifts (6) are expressed in p.p.m. downfield shifts of the methyl groups in the stereoisomericequat ori a1 conformation. Derwes, and D. G. Roux, ibid., p. 783; H. G. KrisGnamuity,3689; B. G. Bolger, A. Hirwe, K. G. Marathe, E. M. Philbin. M. A.Vickars, and C. P. Lillya, Tetrahedron, 1966, 22, 621.The for substituted aromatic carbon atoms T. R. Seshadri, and D. G. Roux, Tetrahedron Letters, 1965,* Positive values represent shifts to lower field. l4 Ref. 1, p. 84.15 Ref. 2, p. 115.l7 Ref. 2, p. 188.Is Ref. 2, p. 97.K. Hanaya, S. Onodera, S. Awano, and H. Kudo, Bull. 18 Y . Senda and S. Imaizumi, Tetrahedron, 1975, 81, 2905.Chem. SOC. Jafian, 1974, 47, 609.l2 J. W. Clark-Lewis, T. M. Stopwood, and L. R. Williams,PYOC. Chem. SOC., 1963, 20; J. W. Clark-Lewis, T. M. Stopwood,and L. R. Williams, Austral. J. Chem., 1963, 16, 107.R. A. Friedel and H. L. Retcofsky, J. Amer. Chem. Sot.,1963, 85, 1300220 J.C.S. Perkin Ifrom internal Me,Si. Each observed chemical shift is been previously reported; (l),20 (2),21 (3),2a (4),2*estimated to be accurate to within &0.06 p.p.m. (6),24 (7),11 (8),25 and (9).2s . . . . . , . .MateriaZs.-hll compounds employed in this work havezo F. Strauss and L. Lemmel. Ber.. 1921. 54. 25.[6/316 Received, 4th June, 19761T. Kusama and D. Koike, .Ni#pon Kaguku Zasshi, 1961, 72,2s G. D. Thakar, N. Janaki, and B. C. Subba Rao, Indian J .F. Arndt and J. Pusch, Ber., 1926, 58, 1648.083. 2s K. Hanaya and K. Furuse. Nippon Kagaku Zasshi, 1968,89,26 S. Mitsui and A. Kasahara, Ni#pon Kagaku Zasshi, 1968,79,22 K. Hanaya, Nippon Kagakzs Zasshi, 1966, 87, 995. 1002.Chem., 1966, 8, 74. 1382
ISSN:1472-7781
DOI:10.1039/P19770000217
出版商:RSC
年代:1977
数据来源: RSC