Efficient synthesis of pyrimido[1,2-c] [1,3]benzothiazin-6-imines and related tricyclic heterocycles by S(N)Ar-type C-S, C-N, or C-O bond formation with heterocumulenes.

A simple and practical synthetic method of pyrimido[1,2-c][1,3]benzothiazin-6-imines and related tricyclic heterocycles has been developed. Treatment of 2-(2-haloaryl)tetrahydropyrimidines with NaH and a heterocumulene such as carbon disulfide, isothiocyanates, and isocyanates in DMF provides the desired cyclization products through a regioselective S(N)Ar-type reaction. This method provides direct access to PD 404182 and related compounds.