Chemo- and regioselective [3 + 2]-cycloadditions of thiocarbonyl ylides: crystal structures of trans-8-benzoyl-1,1,3,3-tetramethyl-7-trifluoromethyl-5-thiaspiro[3.4]octan-2-one and trans-3-benzoyl-2,2-diphenyl-4-(trifluoromethyl)tetrahydrothiophene

Abstract

The title compounds, C19H21F3O2S and C24H19F3OS, were prepared via chemo- and regioselective [3 + 2]-cycloadditions of the respective thiocarbonyl ylides (thiocarbonyl S-methanides), generated in situ, with (E)-4,4,4-trifluoro-1-phenylbut-2-en-1-one. The thiophene ring in the crystal structure of each compound has an envelope conformation. The largest differences between the two molecular structures is in the bond lengths about the quaternary C atom of the thiophene ring; in the spirocyclic structure, the C—C bonds to the spiro C atom in the cyclobutane ring are around 1.60 Å, although this is also observed in related structures. In the same structure, weak intermolecular C—H...X (X = S, O) interactions link the molecules into extended ribbons running parallel to the [001] direction. In the other structure, weak C—H...π interactions link the molecules into sheets parallel to the (010) plane.

Keywords

• crystal structure
• tetrahydrothiophene
• [3 + 2]-cycloaddition