SMALL RING COMPOUNDS-XLI. CYCLOBUTENE CYCLOADDITIONS; SYNTHESIS AND REACTIVITY IN THE BICYCLOHEXAN-2-ONE SERIES

Article abstract of DOI:10.1016/S0040-4020(01)88564-1

Cyclobutene, prepared by base-induced elimination from tosyloxycyclobutane 19 undergoes cycloaddition with ethyl propiolate in the presence of AlCl3 to provide ethyl bicyclo<2.2.0>hex-2-ene-2-carboxylate 20.This cycloadduct at room temperature and in the presence of AlCl3 undergoes forbidden ring opening into ethyl cyclohexa-1,3-diene-2-carboxylate 21.The cycloaddition of cyclobutene with dichloroketene provides 3,3-dichlorobicyclo<2.2.0>hexan-2-one 24 and after reductive halogen removal the endo 3-chloro bicyclo<2.2.0>hexan-2-one 28 (the first study of this strained system).However, further dechlorination of 28 results in rearrangement and fragmentation reactions.