REACTION OF N-ALKYLPYRIDINIUM SALTS WITH PHOSPHORUS TRICHLORIDE

1-Alkylpyridinium bromides 1 having activated N-methylene group react with phosphorus trichloride to give N-(dichlorophosphinomethylene)pyri dinium ylides 2. The site of the reaction in 1,2-dialkylpyridinium hal ides 3 under these conditions is determined by the relative activation of 1- and 2-methylene groups; in the absence of sufficient activation of N-methylene group, reaction occurs at the 2-methylene group to giv e dichlorophosphinylated anhydrobases 5 and 11. 1,4-Dialkylpyridinium bromide 13 behaves analogously to give the corresponding dichlorophosp hinylated anhydrobase 14.