Abstract
The crystal structures of 2-((dimethylamino)carbonyl)-6-(2-thienyl)-2H-thiopyran-3-carboxylic acid (I) and 2-((dimethylamino)carbonyl)-6-(2-furyl)-2H-thiopyran-3-carboxylic acid (II) have been determined by single-crystal X-ray diffraction. Both the compounds crystallise in monoclinic system, but in different space groups. The crystals data are: (I) a=6.5464(1), b=7.5651(2), c=27.6851(7)Å,β=96.867(1)°, Z=4, space group P21; (II) a=10.2683(2), b=10.6690(3), c=12.3477(3)Å,β=101.773(1)°, Z=4, space group P21/c. Substitution of the thienyl- (I) by the furyl-group (II) in the 2H-thiopyrans dramatically changes interactions between the molecules in solid state. The packing for these compounds and the hydrogen bond network are different. The crystals of the thienyl-derivative (I) have an inclination towards a twinning, which could be explained by some features of the packing. The X-ray analysis indicates that the mechanism for the formation of 2-thienyl and 2-furyl substituted 2H-thiopyrans in the reaction of enaminothiones (dienes) with maleic anhydride occurs via a rearrangement of the preliminarily formed endo-cycloadducts and five-membered transition state.
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