Synthesis and structure of novel 1lambda4,2,6-thiadiazines

S,S-Disubstituted sulfodiimines 9 are known to be versatile building blocks for the synthesis of various sulfur-nitrogen-containing heterocycles. Addition-condensation reactions of 9 with three different activated carbonylsubstrates 14-16 lead to several new 1lambda(6),2,6-thiadiazine-3-ones 17-20. S-Debenzylation via a novel synthetic approach utilizing different electrophiles such as TMSCl, Alk(3)O(+)BF(4)(-), Tos(2)O, and Mes(2)O gives rise to a variety of so far hardly known 1lambda(4),2,6-thiadiazine-3-ones 25 and 26. Structure elucidation reveals NH/CH tautomers in solution as well as a tetrahedral asymmetric sulfur attached to the conjugated planar N/C skeleton. The structural features of the 1lambda(4),2,6-thiadiazines 25 and 26 as well as their reactivity toward certain electrophiles will be discussed in detail. Alkylation with Alk(3)O(+)BF(4)(-) preferably results in formation of the 3-alkoxy-1lambda(4)-2,6-thiadiazines 29. In the presence of acid or base, also the N-2-alkyl isomers 30 are formed. Mesylation of 26 with methanesulfonic acid anhydride followed by aminolysis furnishes a variety of the desired heterocycles 5 in moderate overall yield.