Synthesis and Downstream Reactions of 2-(Triphenylphosphino)-4,5-dicarbomethoxy-1,3-diselenole Tetrafluoroborate:  X-ray Crystal Structure of a Nitroso Derivative of a 2-Ylidene-1,3-diselenole Stabilized by an Intramolecular O···Se Interaction

The title 1,3-diselenole Wittig reagent 9 has been synthesised by a new, efficient route from readily-available starting materials and reacted with a variety of functionalized aldehydes to form the corresponding 2-ylidene-1,3-diselenones 12 in respectable yields. X-ray analysis of a nitrosated derivative 14e, prepared by the reaction of 12e with isoamyl nitrite, has provided the first direct evidence for the stabilization of such systems by intramolecular oxygen-selenium interactions.