The Preparation and Properties of 1,2-Bis (triphenylphosphoranyl) benzocyclobutene

The preparation of trans-1,2-bis(triphenylphosphonio)benzocyclobutene dibromide and its conversion to 1,2-bis(triphenylphosphoranyl)benzocyclobutene are described. Treatment of the dibromide salt with base followed by reaction with a benzaldehyde affords different results that depend upon the nature of the solvent. In ethanol as the major solvent, the principal products are the cis- and trans-1-benzylidenebenzocyclobutenes corresponding to the particular benzaldehyde used, together with triphenylphosphine oxide; in DMF or DMSO, the major products are the cis,cis- and/or cis,trans- and/or trans,trans-1,2-bisbenzylidenebenzocyclobutenes corresponding to the benzaldehydes used, as well as triphenylphosphine oxide. In both instances a number of minor products are obtained. The structure and stereochemistry of the major products are in accord with the chemical and physical data reported herein.