Generally, arylmethylene-cyanoacetic acid derivatives react with enols and aromatic or heteroaromatic hydroxy compounds to afford 2-amino-4H-pyran derivatives of type 6. In contrast, a ring closure with the nitrogen atom of the thiadiazole ring occurs when 2-phenacyl-1,3,4-thiadiazoles (1a - d) act on derivatives of arylmethylene-cyanoacetic acid giving rise to the formation of 7H- [1,3,4]thiazolo[3,2-a]pyridine derivatives 5a - r. The same products are obtained if 2-phenacyl-1,3,4- thiadiazoles react with aromatic or heteroaromatic aldehydes and cyanoacetic acid derivatives. The constitution of the novel compounds 5 has been confirmed by an X-ray analysis of 5a.
