Abstract
Dialkyl acylphosphonate acted as an acylating agent for the 2-methyl group in 1, 3, 4-thiadiazolium salts, as well as 2-methylthiazolium and thiazolinium salts, to give 2-acylidenethiadiazoline derivatives. The reaction of diethyl benzoylphosphonate (1) with 5-amino-2, 3-dimethyl-1, 3, 4-thiadiazolium iodide (2c) gave the N-monobenzoate inner salt (6), C-monobenzoate (7), C, N-dibenzoate (8) and 5-benzoylamido-2-styryl-thiadiazolium hydroxide inner salt (9) ; the extent of N-acylation was greater than that of C-acylation. The structures of the inner salt products (6 and 9) were confirmed by an alternative synthesis. A proposed mechanism for the acylphosphonate reaction with 2-methyl-1, 3, 4-thiadiazolium salts is presented, and is consistent with the 13C-nuclear magnetic resonance chemical shifts of the 2-methyl groups of the 1, 3-azolium salts.
