The Cycloadditions Of 1-iminylphosphirane Complexes With Allenes

The ring expansion is a key feature of strained three-membered rings,such as cyclopropanes,aziridines and oxiranes.These small rings participate in intramolecular or intermolecular[3+2],[4+2],[5+2]cycloaddition reactions with olefins,alkynes and allenes.The metal catalyzed carbonylative ring expansions of three-membered rings are important routes to synthesize various cyclic ketones,lactones,and lactams.Our group has been reported the rearrangement reactions of1-acylphosphiranes and 1-iminylphosphiranes with olefins upon heating to afford various bicyclic phosphacycles.In this dissertation,we described a cascade carbonylative ring expansion and cycloadditions of 1-iminylphosphirane complexes with allenes.In the presence of Mo?CO?₆,the carbonylative ring expansion of 1-iminylphosphirane complexes provide an azaphosphacyclohexone complex intermediate with a C=P double bond.Only[4+2]cycloaddition products can be obtained when the intermediate reacts with olefins.However,the reaction of 1-iminylphosphirane complexes,allenes and Mo?CO?₆ provide both[4+2]and[2+2]products.The selectivity between[2+2]and[4+2]cycloaddition reactions could be impacted by modulating the aromaticity of substituents on imino carbon.More aromatic benzenoid resulted in the highly selective formation of the[2+2]cycloadducts.These[2+2]cycloadditions with1,1'-diarylallenes proceeded exclusively at the less substituted double bond.The phosphorus atom attached to the central sp carbon of the allene.In the case of less aromatic thienyl and naphthyl substituted 1-iminylphosphirane complexes,the results of the reaction with allenes are a little complicated.The selectivity between[2+2]and[4+2]cycloaddition reactions was decreased with 1,1'-diarylallenes.The[4+2]cycloadditions became more facile than the competing[2+2]cycloadditions with less steric hindrance allene.Electron donating group on 1-iminylphosphirane complexes improved the reaction and give good reaction yields.No obvious electronic effect of allenes to the reaction was observed.This reaction did not proceed with electron-poor allenoate.