The investigation of an efficient synthesis of bicyclobutane and cyclobutane monomers

Abstract

The synthesis of bicyclobutane and cyclobutene monomers has been studied for the past 30 years. The polymers of these monomers have shown to possess superior properties in comparison to their linear analogs. Current synthetic methods used for the preparation of bicyclobutane and cyclobutene monomers require high temperature, high pressure, a large number of steps, and handling of toxic materials. Generally the synthetic methods employed have given very low yields. Dipolar [2+2]-cycloaddition reactions between alkenes take place spontaneously when one alkene contains strong donor substituents and the other strong acceptor substituents. Our general synthetic scheme involved a [2+2]-cycloaddition to form cyclobutane derivatives containing an acidic proton at C₃ or C₂ and an electron donating substituent at C₁. Following transformation of the donor substituent to a leaving group, bicyclobutanes or cyclobutenes were formed by 1,3- or 1,2-elimination. Phosphite, acetal, and amide as electron-donor substituents in [2+2]-cycloaddition reactions with cyano- or ester-substituted electrophilic alkenes form a variety of cycloadducts.