Migration tendencies of alkyl groups in the rearrangements of lithium trialkyl ethynyl borates: semi-empirical analysis of the transition state

Abstract

The iodine induced rearrangement of lithium alkynylborates yields substituted acetylenes in high yield. The facile control of stereochemistry in these reactions gives them considerable synthetic utility. The product determining step is a 1,2-migration of an alkyl group from boron to an adjacent carbon. The relative migration tendencies of a variety of alkyl groups were calculated and compared with experimental data using the conductor-like screening model (COSMO) for real solvents at the AM1 semi-empirical level. It was concluded that the major influence on migration tendencies is steric strain.