Relative Migratory Aptitudes of Alkyl Groups in the Iodination of Ethenyltrialkylborates. A Conformational Analysis

Article abstract of DOI:10.1021/jo00135a013

Relative migratory aptitudes of various alkyl groups have been determined in the iodine-induced rearrangement of bromomagnesium ethenyltrialkylborates.Trialkylboranes of types R_3-nBR'_n, B-R-9-BBN, and CH(CH3)2C(CH3)2BRR' were complexed with vinylmagnesium bromide and then iodinated.Alkyl rerrangement to the ethenyl terminus, followed by deiodoboration, produced a mixture of 1-alkenes.The overall migratory aptitude order is cyclohexyl > sec-butyl > isobutyl > n-butyl, bicyclooctyl > thexyl.The magnitude of the migratory aptitude ratios after statistical correction varies with the alkyl substitution pattern in the borate.The migration order is most conveniently explained by consideration of relative conformational stability in the iodinated intermediates before rearrangement.