On the Reaction of Dialkyl Acylphosphonate with 2-Methylthiazolium Salts

Dialkyl acylphaphonate worked as an acylating agent on the 2-methyl group of the 2-methylthiazolium and thiazolinium salts in the presence of the bare, to give 2-acylidenethiazoline and thiarolidine derivatives respectively.Dialkyl [ i -awl (alkyl)-1-diaIkylphaphatomethyl]phorphonate war also isolated as a by-prcduct in the same reaction.For example, he reaction of 2,3-dimethylthiazolium iodide with diethyl benzoylphaphonate in the presence of 1,s-diazabicyclo[5,4,01-5-undecene in the dimethylformamide suspension at -20°C gave 2-(3-methyl-2-thiazolinylidene)ecetophenone i n 73% yield and diethyl a-diethylphmphatoben~~lphaphonate.Dialkyl acyl phorphonate afforded 2-a~~lidenethiazoliner in better yield cmpared with acylchlorides and showed the apparent affinity to the carbanions.Application of diethyl benzoylphaphonate to i,2,3-trimethylbenzimidazolium iodide, however, formed a dimeric salt, 1 ,1',3,3'-tetramethyl-2,2'-(2-phenyltrimethylene)-bi~(benzimidazolim)diidide in addition to 2-(1 ,3-dimethyl-2-benzimidazolinylidene)acetophenone.O n the baris of the difference of the reactivity between the 2-methylthiarolium and 2-methylimidarolium r a l h and the kinetic experiments, the mechanism of the acylating reaction war proposed.