Clear-cut difference in the rearrangement of 1-bromo-2-(2-phenyl-3-butenyl)benzene under anionic or radical conditions

Abstract

The o-(3-butenyl)phenyl system bearing a phenyl group on the 2-position of the side chain was studied as a potential mechanistic probe for distinguishing between radical and carbanion intermediates. The Bu3SnH reduction of 1-bromo-2-(2-phenyl-3-butenyl)benzene, 4, yields mainly the 1,5-cyclization product, 6, with a preference for the trans-isomer. Treatment of 4 with Mg or t-BuLi leads to double-bond isomerization and yields (E)-1,2-diphenyl-2-butene, 8, along with 3,4-diphenyl-1-butene, 5.