Regioselective heterocyclization of mixed phosphonium-iodonium ylides with acetylenes involving dimethyl acetylenedicarboxylate

A new approach to the synthesis of λ 5 -phosphinolines was developed consisting in the reaction of mixed phosphonium-iodonium ylides with acetylenes in the presence of dimethyl acetylenedicarboxylate as a dipolarophile. The heterocyclization process under these conditions was found to be regioselective and chemoselective, giving only one of the possible isomers for both internal and terminal acetylenes. The structure of phosphinoline based on internal alkyne, 1-phenylpropyne, was confirmed by single crystal X-ray diffraction analysis. The EPR showed the presence of radical intermediates in the reaction.