1,2-Dihydrobenzocyclobutene (‘benzocycflobutene’): lithiation, and the preparation of some 3-substituted derivatives

Abstract

Treatment of 1,2-dihydrobenzocyclobutene (‘benzocyclobutene’) with n-butyl-lithium–tetramethylethylenediamine in ether gives a mixture of the 1-, 3-, and 4-lithio- and 1,2-dilithio-species; initially the 1- and 3-lithio-species are mainly formed, in roughly equal amounts, but if the reaction is prolonged the 3-lithio-derivative predominates. Treatment of the mixture with chlorotrimethyl-silane or -stannane has given samples of 1- and 3-trimethylsilyl- and -stannyl-1,2-dihydrobenzocyclobutene and 1,2-bis(trimethylsilyl)-1,2-dihydrobenzocyclobutene. Cleavage of the 3-trimethyl-silyl- and -stannyl derivatives with bromine and with iodine monochloride has given 3-bromo- and 3-iodo-1,2-dihydrobenzocyclobutene, and cleavage of the 3-trimethylsilyl compound with mercury-(II) acetate has given the 3-acetoxymercuri-compound.