THE STEREOCHEMISTRY AND MECHANISM OF HYDRIDE REDUCTIONS OF CYCLOHEXENE OXIDES.

Although the ring opening reactions of epoxides have been investigated rather extensively, the reduction of substituted cyclohexene oxides by the complex metal hydrides has until recently received little attention. In the present work, the mixed cis and trans isomers and the pure trans isomers of 1,4-dimethylcyclohexene oxide, 1-methyl-4-t-butylcyclohexene oxide and 4-t-butylcyclohexene oxide were prepared and reduced by the complex metal hydrides. The metal hydrides investigated included lithium aluminum hydride the mixed hydride 3 LiAlH41 AlCl3 sodium, lithium, and potassium borohydrides and diborane. The diborane reduction of 1-methylcyclohexene oxide and 1,2-dimethylcyclohexane oxide was also studied. The reductions, where possible, were carried out in ethereal, alcohol, and hydrocarbon solvents in order to access their effect on the course of the reactions. Reaction products were characterized by infrared spectroscopy and vapor phase chromatography. Results indicate that conformational effects are quite important in determining product distributions when lithium aluminum hydride was employed in ethereal solvents. The increased specificity of the mixed hydride reduction in ether over LiAlH4 in ether was attributed to electrophilically assisted ring opening by aluminum hydride. Both solvent and conformational effects are important in determining product distributions in the alkali metal borohydride reductions in various solvents. There appears to be a steric interaction between the epoxide and the entering solvated hydride donor which is quite important. Author