Relative Migratory Aptitudes of Alkyl Groups in the Iodination of Lithium Ethynyltrialkylborates

Article abstract of DOI:10.1021/jo00324a020

Relative migratory aptitudes of various alkyl groups have been determined in the iodine-induced rearrangement of lithium ethynyltrialkylborates.Trialkylboranes of types R3-nBR'n and thexyl-BRR' were complexed with lithium acetylide-ethylenediamine.Iodination, followed by deiodoboration of the rearranged intermediates, produced 1-alkynes in amounts which depend, after statistical correction, on the relative rates of alkyl group migration in an intramolecular competition.In some cases, the migratory aptitude was found to depend on the alkyl substitution pattern in the organoborate.The overall migratory aptitude order is bicyclooctyl > n-butyl > cyclohexyl, isobutyl, sec-butyl > thexyl.When the secondary and primary migrating carbon series are considered separately, the order is consistently bicyclooctyl > cyclohexyl > sec-butyl, and n-butyl > isobutyl.