Synthesis of Brominated Allenic, 1-3-Butadienyl, and Cyclobutenyl Diphenylphosphine Oxides

摘要

It is known that the halogenation of allenic phosphine oxides leads to the formation of stable phos-pholene salts [1, 2]. Allenic phosphine oxides are intermediates in the synthesis of cyclobutenyl phosphine oxides [3]. In this work we found that the reaction of the brominated allenic diphenylphosphine oxide I, II with bromine occurs via the intermediate formation of unstable phospholene salts. The latter easily eliminate hydrogen bromide to afford 1,2-dibromo-3-tert-butyl(phenyl)-1,3-butadien-1-yldiphenyl-phosphine oxides III, IV, which isomerized into the corresponding cyclobutenes V, VI when refluxed in toluene. These compounds contain the bromine atoms both at the double bond and at the saturated carbon atom. Therefore they are of interest to study further transformations of cyclobutene carbocycles.