Synthesis of Highly Branched Sulfur−Nitrogen Heterocycles by Cascade Cycloadditions of [1,2]Dithiolo[1,4]thiazines and [1,2]Dithiolopyrroles

We report the synthesis of some new polysulfur−nitrogen heterocycles by cascade cycloadditions to readily available polycyclic 1,2-dithiole-3-thiones. Thus, treatment of bis[1,2]dithiolopyrrole dithione 1 with dimethyl acetylenedicarboxylate (DMAD) or dibenzoylacetylene (DBA) gave the 1:4 adducts 2a,b and 3a. On the other hand, cycloaddition of bis[1,2]dithiolo[1,4]thiazine dithiones 4ad with the same dipolarophiles gave the 1:2, 1:3, or 1:4 adducts 5ac, 6a, 7a, 8a, 9a, and 10a,c,d selectively in fair to high yields. Reaction conditions were crucial for achievement of selectivity in thermal reactions. Catalysis by scandium triflate was used in the reaction of 4a and 2 equiv of DMAD. Treatment of the [1,2]dithiolo[1,4]thiazine dithione 11 with DBA gave the 1:2, 1:3 (two isomers), and 1:4 adducts 1214 and 15ad selectively. Cyclic voltammetry of selected examples showed irreversible processes that were not influenced by peripheral groups bonded to the heterocyclic system.