J. Org. Chem., Vol. 39, No. 10, 1974
Notes lution and then water and evaporated to give an oil (4.6 g). The latter was chromatographed over silica gel (100 g) and the desired product (1.3 gj was eluted with mixtures of 5-10% ethyl acetate in methylene chloride. The material showed a single peak on glc analysis [Rf 14.2, 205" (10 ft X 0.25 in., 5% QF-1 on Chromosorbj] and its infrared spectrum [1660 (carbonyl) and 1605 cm-I (double bond)] was identical with that of a specimen prepared according to a known method.8 Its mass spectrum showed a molecular ion at m / e 164 and the base peak at m / e 136 (M - 28). Other significant peaks appeared at m / e 122, 108,93, 79,41, and 39. Cyclization of Citronellonitrile (23). Citronellonitrile (23, 24.4 gj and triethyloxonium fluoroborate (30.8 g) were heated together at 80" with stirring under dry nitrogen for 3 hr. Water (150 ml) containing acid (10 ml) was added and the mixture, after being stirred for a few minutes, was steam distilled. The distillate was neutralized using sodium bicarbonate and the product (6.32 g, 25%), a colorless oil with a peppermint odor, was isolated by extraction with methylene chloride. Glc analysis (5 ft X 0.25 in. column, Mcn'air's phase, 30% on 60-80 mesh Chromosorb, 125", He flow rate 75 ml/minj revealed the presence of six components: A (Rf 5.8, sa), B (Rf 13.2, 44.6%), C ( R f 15.4, 19.7%), D (Rf 18.5, 4.2%), E (Rf 22.2, 6.3%j, and F (R, 26, 16.37~).Mass spectral data were obtained for each of these compounds. Component A showed parent ions (low-voltage study) at m / e 150 and 180 and was assumed to be a mixture. It and components D and E, both of which showed m / e 180 peaks for their parent ion, were not studied further. Components B and C, both with parent ions at m / e 154, were identified as methone and isomenthone, respectively, by comparison of their infrared spectra and Rf values, while component F by the same criteria, proved to be pulegone (parent at m / e 152, ir 1690 and 1625 cm-I).
1437
Table I H y d r o b o r a t i o n - O x i d a t i o n of 1 - H e x e n e U s i n g BMS. Solvent Study. Solvent
E t h y l ether Tetrahydrofuran Hexane Toluened Methylene chlorided E t h y l acetated Acetonitrile d
1-Hexanol,
2-Hexanol,
7ob
7oh
%'
94.4 93.6 94.1 94.2 93.6 94.2 93.8
5.6 6.4 5.9 5.8 6.4 5.8 6.2
100 100 100 98.1 99.4 100 80.9
Total yield,
a All reactions involved t h e addition of BMS (11 mmol) t o 1-hexene (30 mmol) dissolved in 10 ml of solvent a t 0-5". After 1 hr a t 20-25", t h e reaction mixture was oxidized with alkaline hydrogen peroxide. Relative a m o u n t by gc analysis. total yield by gc analysis using a n internal standard. d E t h a n o l (10 ml) added a s cosolvent prior t o oxidation.
BMS is now commercially available a n d appears t o be a useful borane reagent for organic synthesis.2 However, a systematic investigation of t h e hydroboration of alkenes with BMS has not been reported. S u c h a s t u d y will now be described herein. T h e miscibility of BMS with various solvents prompted a n examination t o determine if t h e solvent h a s any effect on the hydroboration of alkenes with BMS. 1-Hexene was chosen as a representative alkene. T h e s t a n d a r d procedure Registry No.-l6 (R = R' = H), 5048-19-1; 19, 2359-64-0; 20, and t h e results of this solvent s t u d y are given in T a b l e I. 51004-10-5; 22, 19198-29-9; 23, 51004-11-6; 24, 51004-12-7; 29, 51004-13-8; triphenylmethylphosphonium bromide, 1779-49-3; 2As in t h e case of borane-tetrahydrofuran,2 hydroboraQ3-cyanoethyl)cyclohexanone, 4594-78-9; 2-(~-cyanoethyl)cyclo- tion of a monosubstituted alkene with BMS proceeds heptanone, 33736-92-3; 2-cyanomethylcyclopentanone~51004-14-9; quantitatively, placing boron 94% in the terminal position triethyloxonium fluoroborate, 368-39-8. and 6% in t h e secondary position. Surprisingly, the use of References a n d Notes various solvents, most of which could not previously be R. K . Hill and R T. Conley, J. Amer. Chem. SOC.,82, 645 (1960) used in hydroboration reactions, presented no problems R . T . Conley and B. E . Nowak. J. Org. Chem.. 26, 692 (1961) for t h e hydroboration with BMS. Solvents such as ethyl R T . Conley and 8. E. Nowak. J. Org. Chem.. 27, 1965, 3196 (1962). ether, hexane. toluene, a n d methylene chloride. in which R M . Black and G . E. Gill, J. Chem. SOC. C, 671 (1970) BH3 has low or negligible solubility, readily dissolve BMS T . Sasaki, S. Eguchi. and T Toru, J . Amer. Chem. SOC., 91, 3390 (1969). t o give quantitative hydroborations. E v e n solvents which The formation of such species using triethyloxonium fluoroborate is react with diborane c a n be used for hydroborations with well known in the literature, see H Meerwein. P Lasch, R Merach, and J . Spille, Ber., 89, 209 (1956) B M S ; e.g., 1-hexene was hydroborated cleanly a n d q u a n G . Stork, A Brizzolara, H . Landesrnan, J Smuszkovicz, a n d R . Tertitatively in ethyl acetate. rell, J. Amer. Chem. SOC.,85, 218 (1963) To define more fully t h e utility of BMS as a hydroboR . Granger, J . - P Chapat, J. Crassous, F.Simon, and H Viols, Bull. SOC.Chim. f r . . 4265 (1968) rating agent, a series of representative alkenes were alF B. Laforge, N Green, and W. A . Gersdorff, J , Amer. Chem. lowed t o react with BMS in a n appropriate solvent. HexS O C . , 70, 3707 (1948) L F . Fieser. "Experiments In Organic Chemistry," 3rd e d , D. C. ane was chosen as t h e solvent because a n inexpensive Heath, Boston, Mass.. 1955, p 84. grade is commercially available a n d is of sufficient purity t o require no prior t r e a t m e n t . T h e results of this study, a s shown in T a b l e 11, indicate that t h e hydroboration-oxidation of alkenes with BMS in a hydrocarbon solvent is a general reaction a n d gives exOrganic S y n t h e s i s U s i n g B o r a n e - M e t h y l Sulfide. The cellent yields of t h e corresponding alcohols. T h a t t h e H y d r o b o r a t i o n - O x i d a t i o n of A l k e n e s reaction is both regioselective a n d stereoselective was shown by t h e hydroboration-oxidation of l-methylcycloClinton F. Lane pentene (eq 1). Aldrich-Boranes, Inc., a Subsidiar-31 of the Aldrich Chemical Cornpan), Inc., ,Viluauhee, Wiscor?sin53233 Received December 6, 1973
Borane-methyl sulfide (BMS) is a stable, liquid BH3 complex, a n d its n u m e r o u s advantages over borane-tetrahydrofuran solution a s a storable reagent were discussed by A d a m s a n d coworkers.l T h e m a i n advantages are t h a t (1) BMS h a s a molar concentration of borane t e n times t h a t of borane-tetrahydrofuran solution, (2) BMS is soluble in a n d unreactive toward a wide variety of aprotic solvents, a n d (3) BMS is apparently stable indefinitely when refrigerated.
U
100% yield, > 99% trans
T h e synthetic utility of this new hydroboration-oxidation procedure was further demonstrated by treating 01 a n d @-pinenewith BMS on a molar scale in hexane. From (-)+-pinene an 85% isolated yield of (-)-cis-myrtanol
1438 J. Org. Chem., Vol. 39, No. 10, 1974
Notes
Table I1 H y d r o b o r a t i o n - O x i d a t i o n of A l k e n e s Using BMS" Relative amounts,
Time, hrb
Alkene
1-Hexene
1
2-Methyl-lpentene trans-3-Hexene
1
Styrene
1 3 1
Cyclopentene Cyclohexene
1 1
Alcohol products
%d
1-Hexanol 2-Hexanol 3-Methyl-lpentanol 3-Hexanol
93.6
2-Phenylethanol 1-Phenylethanol C yclopentanol C yclohexanol
86.3 13.7
1
99.8
1
>99f >99f
100
exo-Norborneol trans-2-Methylcyclopentanol
l e
88.4 100 100 96.5 78.7 100 87 94 86.4
le 1-Methylcyclopentene
100
6.4
1 6
Norbornene
Total yield,
a All reactions involved the addition of BMS (11 mmol) t o the alkene (30 mmol) dissolved in 10 m l of hexane a t 0-5'. After an appropriate interval, ethanol (10 ml) was added a n d t h e reaction m i x t u r e was oxidized using 3 N aqueous N a O H (11 mmol) a n d 30% aqueous HzOz (33 mmol). T i m e for hydroboration a t 20-25'. B y gc analysis. d By gc analysis using a n internal s t a n d a r d . e Reaction mixture was heated t o reflux for 1 hr t o ensure complete hydroboration. f
