A new access to diazaphospholes via cycloaddition-cycloreversion reactions on triazaphospholes.

A novel bis-CF 3 -substituted diazaphosphole was synthesized selectively from hexafluoro-2-butyne and a 3 H -1,2,3,4-triazaphosphole derivative. The [4+2] cycloaddition and subsequent cycloreversion reaction under elimination of pivaloyl nitrile affords the product in high yield. The heterocycle coordinates via the phosphorus atom to a W(CO) 5 -fragment and shows stronger π-accepting properties than the triazaphosphole.