α-Difluoromethylenephostones by Iodocyclization

Significance

The synthesis of a biological relevant class of cyclic α-difluoromethylenephosphonates (phostones) utilizing a mild and regioselective iodocyclization of β-allenic phosphonates in moderate to high yields is reported. The starting β-allenic phosphonates are readily prepared from propargylic tosylates. A mechanism involving iodine-initiated, thermodynamically favored endo cyclization is proposed. Relative facility of the reaction may be rationalized on the basis of stability and steric factors involved in the formation of the iodonium intermediate.