Reaction of acetylenic esters and N-functionalized phosphazenes. 1,2- versus 1,4-addition of N-vinylic phosphazenes

Abstract

Reaction of phosphazenes derived from aminophosphonates with acetylenic esters leads to conjugated phosphorus ylides. The formation of these stabilized ylides is explained through a [2+2] cycloaddition reaction of the PN linkage of the phosphazene (1,2-addition) and the triple bond of the acetylenic ester followed by ring opening of the azaphosphete intermediate. However, in the case of N-vinylic phosphazenes, the phosphazenes derived from triphenyl- and trimethyl-phosphine react as enamines (1,4-addition) with diacetylenic esters, whereas in phosphazenes derived from trimethylphosphine a 1,2-addition of ethyl propiolate to the PN linkage of the phosphazene is produced.