Pyridinium dichlorophosphinomethylides

Seven new pyridinium dichlorophosphinomethylides 2 have been obtained from dichlorophosphinylation of the pyridinium methylides generated in situ. 2 g ive 1,3-bis(alkoxycarbonyl)-2-phosphaindolizines 4 through 1,5-electrocycli zation of the intermediate, bis(pyridinium ylidyl)phosphenium chloride 3 wh ich is generated either from disproportionation of 2 or from the reaction o f 2 with pyridinium methylide. Formation of 3 has been confirmed ky carryin g out a crossed reaction. 3-Substituted 2 forms 4 regiospecifically. Intram olecular 1,5-cyclocondensation of 2-methylpyridinium dichlorophosphinomethy lide is preferred over its disproportionation. (C) 2001 John Wiley & Sons, Inc.