摘要:

1975 93Organoboron Compounds. Part IX. Synthesis and Properties of some2-Phenyl-1,3,2-oxazaborolansBy R. Harry Cragg * and Alan F. Weston, University Chemical Laboratory, Canterbury CT2 7NHThe synthesis and properties of some 2-phenyl-l.3.2-oxazaborolans are described and the i.r. spectra and generalmass-spectral features of these compounds are discussed.RECENTLY there has been renewed interest in the syn-thesis and properties of heterocyclic organoboranes.For example the 2-substituted 1,3,2-diazaboracyclo-alkanes have been reviewed2 and work concerning thedioxa- and dithia-borolans and borinans has beenpublisl~ed.~ iVe have been interested in heterocyclicorganoboranes for some time4-7 and were surprised tofind that with few exceptions the 1,3,2-0xazaborolansappear to have been ignored.We therefore report ourresults concerning the preparation and properties ofthese compounds.RESULTS AND DISCUSSIONTwo general methods were used for the synthesis ofthe 2-phenyl-l,3,2-oxazaborolans : (a) reaction of anaminoakohol with bis(et1iylthio)phenylborane ; and (b)reaction of an aminoalcohol with bis(diethy1amino)-phenylborane. In both cases, one of the products ofthe reaction is volatile and this leads to a very smoothsynthesis of the boron heterocycles. For example 5-methyl-2-phenyl-l,3,2-oxazaborolan was obtained fromthe interaction of 1-methyl-2-aminoethanol and bis-(ethy1thio)phenylborane in benzene solution [equation(l)]. The reaction was stopped when the volatileproducts passed into an aqueous lead(I1) acetate solutionHO-CHMe /O-CHMeB(SEt)ZPh + I - PhB, I t 2EtSH ( 1 )H2N-CH2 N-CH2Hfailed to give any precipitation of lead(r1) hydrogen-sulphide. In a similar way the interaction of bis-(diethy1amino)phenylborarie and 2-amino-2-methyl-propanol gave 4,4-dimet hyl-2-phenyl-l,3,2-oxazaborolanH2N- CMe2 ,N-CMe2 HE(NEt,I,Ph + I - PhB I t 2Et2NH (2)HO- CH2 '0 -CH2[equation (2)].Using method (a), nine 2-phenyl-l,3,2-oxazaborolans were prepared. Also 2-phenyl-l,3,2-oxazaborinan was prepared to enable us to compare theproperties of the five- and six-membered heterocyclicsystems. The physical properties and analytical datafor these compounds are given in the Table.The 2-phenyl-l,3,2-oxazaborolans were all obtained asdistillable liquids ; compounds (VI) and (VII) solidifiedon standing.Attempts to prepare 2-alkylthio-l,3,2-K. H. Cragg and 31. Nazcry, J.C.S. Dalton, 1974, 1438.a K. Niedenzu and C. D. Miller, Fortschr. Chem. Forsck.,S. G. Shore, J. L. Crist, €3. Lockman, J. R. Long, and A. D.R. H. Cragg, J . Inorg. A'uclenr Chem., 1968, 30, 396.1970, 191.Coon, J.C.S. Dalton, 1972, 1123.oxazaborolans were unsuccessful. For example theinteraction of tris(n-propy1thio)borane with 2-amino-ethanol resulted in formation of a polycyclic borazinewithout the isolation of any intermediate compound[equation (3)j. In contrast the interaction of tris-(ethylthio) borane and 2-methylaminoethanol resulted inH, *-CH2 Iformation of the corresponding heterocyclic compound[equation (4)l.MeH,C - NHMe H2C-H2C-OH+ B(SEt13 - I N\B-SEt -!-2EtSH ( 4 IH$ -0'I1.r.S@ctra.--The i.r.- and mass-spectral propertiesof 2-phenyl-l,3,2-diazaborolans and borinans have beendiscussed by Niedenzu and assignments made werev(N-H) at 3 465 cm-l and v(B-N) at 1500 &- 10 cm-l.The appearance of a shoulder on the v(N-H) peak wasinterpreted as being due to some association in thesecompounds. This effect has also been observed for2-phenyl-l,3,2-azathiaborolidine which we discussed inan earlier paper.7 In the present compounds the effectis not so pronounced. The unsubstituted borolan andborinan showed only a slight shoulder. Those withsubstituents at the C(5) position, i.e. the carbon next tothe oxygen atom, showed a slightly greater effect.Thev(N-H) band in compound (IV) was intermediatebetween those of (111) and (1'). In contrast compoundswith substituents at the C(4) position, i.e. the carbonadjacent to the nitrogen atom, showed a more pro-nounced effect, for example (V). In this caw the twopeaks were separated.The effect of C(5) substitution was to lower v(B-0)and the effect of C(4) substitution was to lower v(B-N).Substitution of PhCH, for H on the nitrogen atomcaused a significant increase in v(C-N) in the borolansystem. The v(B-0) and v(B-N) ring vibrations wereconsistent throughout, demonstrating that substitutionhad little effect on the stereochemistry of the ring.The following tentative assignments are made for theR. H. Cragg, Chem.Comm., 1969, 832.K. H. Cragg, J . 1'. K. Husband, and A. I:. Wcston, J.C.S.R. H. Cragg and -4. I;. Weston, J.C.S. Dalton, 1973, 1054. * G. M. Anthony, G. J. W. Brooks, I. Slaclean, and I. Sangster,Dalton, 1973, 668.J . Chromatog., 1969, 7, 62394 J.C.S. DaltonAnalyses, yields, and b.p.s for 2-phenyl- 1,3,2-oxazaborolanslinalyses/o/,CompoundFound Calc.v r- -h----7 I3.p. (O,/"C), Yield/ --h-P/mmHg 04 C H N c: H NH2( 1 1 PhB, FH2 85, 0.1 87 67.15 7.5 8.55 67.1 7.5 8.70/O--C\,O-CH2N-CH2HPhB, I 64, 0.15 56PhB 82, 0.4 86tiphB/'-yH2 so, 0.15 46\N - C H M ~H,O-CH2PhB, I 84, 0.9 50N -CMe2H,O-CHPh I 130, 0.1 70H/O-CCH?9-35 65.3 6.8 9-608-35 67.1 7.5 8.7068-25 G.765.95 i.78.70 3 - 67.16 7-7 8.65 67.1 I ' c )68.6 8.0 8-00 68.4 8.0 7-8074-75 6.6 6-15 75.3 6.3 6.30( Y I I ) PhB' I 128, 0.2 71 75-65 6.9 5.95 75.95 6.8 5-90'N-CH2CH2Ph,O -CHMe(YIIT) PhB\ I 122, 0.1 71 76-3N -CH2CH 2Ph/O-CHz( X I 1 PhE\ I 130, 0.1 69 76.0N-CHMeCH 2Ph/O-CH2N-CH2 Me103, 5 80 87.0 (XI PhB\ Iborolan and borinan ring systems ; the various wave-numbers (cm-l) can be found within the quoted limits.Borolan Borolan + borinanv (N-H) 3 450 & 30 3 450 f 30v (B-N) 1503 f 7 1503 f 8v(B-Ph) 1453 5 7 1457 f 11v (B-0) 1321 f 9 1 334 f 22v(C-N) 1223 & 37 1227 f 42v(C-0) 1099 5 22 1 105 f 28v(B-0) (ring) 698 2 698 f 2v(B-N) (ring) 650 & 5 650 f 5636 f.3 636 f 37.37.57.75.65 76.5 7.2 5-605-70 76.5 7.2 5.608.85 67.15 7.5 8.70intense P - 1 peak formed iria loss of a proton fromC(4).In some cases this was the base peak. Com-pound (V) has both C(4) positions methylated and henceno proton loss can take place by C-H bond cleavagewith respect to the annular nitrogen atom and in thiscompound the base peak was at m/e 160, i.e. P - CH,:a C-C bond p cleavage with respect to the N atom.Doubly charged ions formed from the parent were inthe majority of cases less than 1% of the total ionabundance.* For details see Notice to Authors No. 7, J.C.S. Dalton, 1973,Index issue (items less than 10 pp. are supplied as full-sizc copies).I l k . H. Cragg, G. Lawson, and J. F. J. Todd, J.C.S. Dalton,1972, 8781975 95and borinan follow the general pattern. In the threecompounds with a benzyl group attached to nitrogen,intense peaks at m/e 91, 2.e.the tropylium ion, wereobserved. Methylation of the carbon atom adjacent tothe nitrogen atom, in these borolans, enhanced tro-p ylium-ion formation. The C (5) phenyl-substitutedcompound also showed a peak 33% of the base, assignableto the tropylium ion, and 2-phenyl-l,3,2-oxazaborolanshowed an intense peak due to the tropylium ion whichwas 43% of the base peak. The monomethyl-substi-tuted borolans and the borinan all showed peaks,assignable to the tropylium ion, of ca. 10% intensitycompared to the base peak, whilst dimethyl substitutionreduced the intensity of the peak to ca. 4%. Hencemethylation reduced tropylium-ion formation, irrespec-tive of the position of substitution, by approximately thesame amount and dimethylation reduced it even further.The borinan also formed much less tropylium ion thanthe borolan.The mass spectra of compounds (I), (111), and (IV)all showed peaks at m/e 105, which was shown byprecise mass measurements to be due to C,H,+ ion, in24.3, 13.57, and 1.71y0 abundance compared to the basepeak. There were C5H5+ ions present in all spectra insuch ratios to the C,H,+ ions that all m/e peaks can betaken as completely C,H,+ in tropylium-ion form, andthe metastable ions at 46.4 associated with fragmentationof tropylium ion to cyclopentadienylium were observedin each case.All the compounds had peaks in theirmass spectra at m/e 89 and 63. We find that thesepeaks, by precise mass measurements and metastablescanning, are due to the boratropylium and boracyclo-pent adien ylium ions .12 Although the borat rop yliuinmle 89 mle 63ion has previously been reported for three compound~,~3*14its fragmentation to the corresponding boracyclopenta-dienylium ion appears to be a general process in themass spectra of 2-phenyl-1,3,2-oxazaborolans.EXPERIMENTALSolvents were dried over sodium wire and distilled beforeuse. The mass spectra were recorded using an A.E.I.MS002 mass spectrometer a t 70 eV.* The source wasmaintained at 170 "C and the compounds were introducedas neat liquids or solids using an unheated direct-insertionprobe.1.r. spectra were recorded using a Perkin-Elmer457 spectrometer. Bis(diethylamino)phenylborane,l5 bis-* 1 eV M 1.60 xl2 R.H. Cragg, J. F. J. Todd, R. B. Turner, and A. F. Weston,13 C. Cone, M. J. S. Dewar, R. Golden, F. Maseles, and P. Rona,14 C. J. W. Brooks, B. S. Middleditch, and G. M. ,4nthony, Org.J, 1~ = 1 mol dm-3.J.C.S. Chem. Comnt., 1972, 206.Chem. Comm., 1971, 1522.Mass Spectrometry, 1969, 2, 1023.(ethylthio)phenylborane,le and tris(ethy1thio) borane l7 wereprepared by established methods.2-Phenyl-1,3,2-oxazaborolan.-2-Aminoethanol (1.30 g,0 . 0 2 ~ ) was added slowly to bis(diethy1amino)phenylborane(4-27 g, 0.018~) in benzene (10 cm3). The mixture washeated under reflux for 2 h. After removal of the solventand volatile materials the residue, on distillation, afforded2-phenyl-1,3,2-oxazaborolan (1.39 g, 56y0), b.p.64 "C (0.15mmHg) (Found: C, 65-15; H, 6.6; N, 9.3. Calc. forC,H,,BNO: C, 65.3; H, 6.8; N, 9.5%).3-Benxyl-2-phenyl- 1,3,2-oxazaborolan .- 2-Benzylamino-ethanol (1-06 g, 0.007~) was added slowly to bis(ethy1thio)-phenylborane (1.5 g, 0.007~) in benzene (10 cm3). Themixture was heated under reflux for 3 h after which thesolvent and any remaining ethane thiol were removedin vacuo. The ethane thiol was passed into an aqueouslead(I1) acetate solution where it was precipitated as thelead(I1) hydrogensulphide. The residue on distillationafforded 3-benzyl-2-phenyl- 1,3,2-oxazaborolan (1.22 g,71%), b.p. 128 "C (0.2 mmHg), m.p. 40 "C (Found: C,75-65; H, 6.90; N, 5-95. Calc. for C15H,,BNO: C, 75.95;H, 6.75; N, 5-9o/b).Reaction between Bis(ethy1thio)phenylborane and D L - ~ -0.014~) was added to a solution of bis(ethy1thio)phenyl-borane (2.85 g, 0.014~) in benzene.The mixture washeated under reflux for 3 h. The volatiles were removedin vacuo and the residue was washed with light petroleumand on filtration yielded an unidentified white solid, m.p.124 "C. On removal of the solvent from the washings theresidue afforded, on distillation, 4-methyZ-2-pl~enyl- 1,3,2-oxazaborolan (0.98 g, 45%), b.p. 70 "C (0.15 mmHg) (Found:C, 67.15; H, 7-70; N, 8.65. Calc. for C,H1,BNO: C, 67-1;The reaction of L-2-aminopropan- 1-01 with bis(ethy1thio)-phenylborane was carried out in the above manner. As allthe other 2-phenyl- 1,3,2-oxazaborolans and 2-phenyl- 1,3,2-oxazaborinan were obtained by the above methods, theirphysical properties and analyses are given in the Table.1,2;3,4;5,6-Tris(ethyleneoxy)borazine.- Tris(n-propyl-thio)borane (1.73 g, 0.028~1) and 2-aminoethanol (6.85 g,0.029~) were heated under reflux in benzene for 3 h.Onremoval of the solvent a residue was obtained which onsublimation [lo0 "C (0-5 mmHg)] afforded 1,2;3,4;5,6-tris-(ethyleneoxy)borazine (1.84 g, 92%), m.p. 150 "C (Found:C, 33.8; H, 8.95; N, 19-45; M , 207. Calc. for C,H,,B,N,O,:C, 34.8; H, 8.80; N, 20.3%; M , 207).2-Ethylthio- 3-wethyl- 1,3,2-oxazaboroZan.- Tris (ethylthio) -borane (2.23 g, 0-012M) and 2-methylaminoethanol (0.86 g ,0.012~) were heated under reflux in benzene for 3 h. Onremoval of the volatiles under reduced pressure the residueafforded on distillation Z-ethylthio-3-methyl-1,3, Z-oxaza-borolan (1.39 g, 3%), b.p. 60-63 "C (6 mmHg), 1.4817(Found: C, 41-4; H, 8.35; N, 9.75. Calc. for C,H,,BNOS:aminop ropan- l-ol.-~~-2-Aminopropan- 1-01 (1.02 g,H, 7.45; N, 8.7%).C, 41.4; H, 8.30; N, 9.65%).[3/2330 Received, 13th Novembes., 19731l5 I<. Niedenzu, H. Beyer, and J. W. Dawson, Inorg. Chenz.,l6 R. H. Cragg, 31. F. Lappert, and B. P. Tilley, J . Chem. SOC.1962, 1, 738.( A ) , 1967, 947.. i7 J . Brault and J. M. Lalancette, Canad. J . Chem., 1964, 42,2093

ISSN:1477-9226    

DOI:10.1039/DT9750000093

出版商:RSC    

年代:1975

数据来源: RSC