On the reaction of epoxides with diborane

Abstract

The reaction of some sterically crowded styrene epoxides (phenyloxirans) with diborane has been investigated. (Z)-1-Phenylpropene oxide (cis-2-methyl-3-phenyloxiran) reacts with diborane in tetrahydrofuran at 20° to give, after oxidation, 1-phenylpropan-2-ol(53 %), 1-phenylpropanol (23 %) and 1-phenylpropane-1,3-diol(2%4 ). 2-Methyl-1-phenylpropene oxide (2,2-dimethyl-3-phenyloxiran) under similar conditions affords 2-methyl-1-phenylpropanol (7%) and 2-methyl-1-phenylpropane- 1,3-diol(84%), the major isomer of which was the threo. The epoxide of 2-methyl-3-phenylpropene gives a diol mixture (81%) consisting of the above diols plus 2-benzylpropane-1,3-diol, and 2-methyl- 3-phenylpropanol (3%). The reaction of 1-methyl-2-phenylcyclohexene oxide with diborane gave a complex mixture af products, three of which have been identified. The mechanism of the reaction is discussed with supporting evidence from the use of deuterated diborane.