Carbonium ion rearrangements: electronic and conformational control in the migration of the electronegative group diphenylphosphinyl

Abstract

In contrast to the pinacolyl derivatives (6) and (21), cis- and trans-2-diphenylphosphinyl-2-methylcyclohexyl tosylates (14a and b) give neither methyl nor diphenylphosphinyl migrations on solvolysis. Instead, two different olefins, 3-diphenylphosphinyl-3-methylcyclohexene from (14a) and the 4-diphenylphosphinyl-4-methyl isomer from (14b), are formed in high yield. The conformations of the tosylates and the structures of the olefins were elucidated by deuterium labelling and the use of the n.m.r. shift reagent Eu(dpm)₃. The rates of solvolysis are slow compared with methyl or diphenylphosphinyl migration and it is suggested that electronic and not conformational factors control the corresponding acyclic rearrangements.