New thiopyran-4-spiro-2′-(1,3-dithiolane): Formation mechanism and crystal structure

Ethylene trithiocarbonate reacted with dimethyl acetylenedicarboxylate to furnish tetramethyl thiopyran-4-spiro-2′-(1,3-dithiolane)-2,3,5,6-tetracarboxylate, a new thiopyran-4-spiro-2′-(1,3-dithiolane) heterocyclic compound, as the minor product together with the major product dimethyl 2-thioxo-1,3-dithiole-4,5-dicarboxylate. The new heterocycle was probably formed through a [2 + 2] cycloaddition between ethylene trithiocarbonate and dimethyl acetylenedicarboxylate followed by a 1,3-dipolar cycloaddition or [4 + 2] cycloaddition. Crystal structure of the new compound revealed that the thiopyran ring and 1,3-dithiolane moiety were perpendicular to each other.