Synthesis and structures of stable phosphorus zwitterions derived from mesoionic 4-trifluoroacetyl-1,3-oxazolium-5-olates.

Trialkyl phosphites were evaluated as phosphorus nucleophiles for addition to mesoionic 4-trifluoroacetyl-1,3-oxazolium-5-olates (1), thereby producing tetravalent phosphorus zwitterions (2) in good yields. The structure of 2 was determined to be a tetravalent phosphonium enolate via single crystal X-ray analysis.