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 <b>1</b> with dimethyl acetylenedicarboxylate (DMAD) or dibenzoylacetylene (DBA) gave the 1:4 adducts <b>2a</b>,<b>b</b> and <b>3a</b>. On the other hand, cycloaddition of bis[1,2]dithiolo[1,4]thiazine dithiones <b>4a</b><b>−</b><b>d</b> with the same dipolarophiles gave the 1:2, 1:3, or 1:4 adducts <b>5a</b><b>−</b><b>c</b>, <b>6a</b>, <b>7a</b>, <b>8a</b>, <b>9a</b>, and <b>10a</b>,<b>c</b>,<b>d</b> 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 <b>4a</b> and 2 equiv of DMAD. Treatment of the [1,2]dithiolo[1,4]thiazine dithione<b> 11</b> with DBA gave the 1:2, 1:3 (two isomers), and 1:4 adducts <b>12</b><b>−</b><b>14</b> and <b>15a</b><b>−</b><b>d</b> selectively. Cyclic voltammetry of selected examples showed irreversible processes that were not influenced by peripheral groups bonded to the heterocyclic system.