STEREOSELECTIVITY OF BASE-INDUCED CONVERSION OF EPOXIDES INTO ALLYLIC ALCOHOLS

Very high selectivity is observed in the reaction of unsymmetrical epoxides with lithium diethylamide, leading to allylic alcohols. The proton abstraction occurs most readily from the least substituted carbon in open-chain systems, with large factors separating primary from secondary from tertiary proton abstraction. Thus 2-pentene oxide yields 1-penten-3-ol as the exclusive allylic alcohol product, and 2-methyl-3-heptene oxide gives only 2-methyl-4-hepten-3-ol. Nearly statistical product distribution is observed from 2-methyl-2-butene oxide, which gives 2-methyl-3-buten-2-ol (41%) and 3-methyl-3-buten-2-ol (59%). High selectivity is also observed in the reaction of mixed cis- and trans-3-methylcyclohexene oxide, where at most a few per cent of the trisubstituted olefin product is formed. Conformational effects also play an important role in determining the selectivity of this reaction, as shown by the conversion of trans-4-t-butylcyclohexene oxide into trans-5-t-butyl-2-cyclohexenol (97%), accompanied by only 3% trans-4-t-butyl-2-cyclohexenol. Similar results are obtained with trans-2-octalin oxide. The exclusive formation of contrathermodynamic, least-substituted olefin from the open-chain epoxides is unique among elimination reactions. © 1969, American Chemical Society. All rights reserved.