Studies on chalcogen-containing heterocycles. Part 38: Regio- and stereoselective tandem addition–iodocyclization of 2-ethynylphenyl isothiocyanates with N- and O-nucleophiles affording 4-(iodoalkylidene)benzo[d][1,3]thiazines

The treatment of the o-ethynylphenyl isothiocyanates with primary and secondary amines in 1,2-DCE, followed by the addition of I2 and then heating resulted in the regio- and stereoselective tandem addition–iodocyclization to give the (4E)-2-amino-4-(1-iodomethylidene)benzo[d][1,3]thiazine derivatives as the sole product in high yields via the 6-exo-dig mode cyclization. The 2-alkoxy-1,3-benzothiazines were similarly produced from the o-ethynylphenyl isothiocyanates and the corresponding sodium alkoxides.