Synthesis and Thermal Rearrangement of 7-(1,2-Butadienyl)bicyclohept-2-ene

Article abstract of DOI:10.1021/ja00374a023

A mixture of syn- and anti-7-(1,2-butadienyl)bicyclo<2.2.1>hept-2-ene <1a (30percent) and 1b (70percent)> has been synthesized through a Grignard reaction employing syn-7-bromonorbornene and 3-bromo-1-butyne.Gas-phase pyrolysis of the mixture at 275 deg C for 24 h gives 1-ethylindan (7) as the single isolable product in 28percent yield.This result is interpreted in terms of an initial concerted <_?2_s + _?2_s + (_?2_s + _?2_a)> rearrangement of 1a to 1-ethylidene-3a,4,5,7a-tetrahydroindene (5), which through a series of not less than five allowed <1,5> hydrogen shifts may give 1-ethylindan.