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

The title compounds, C(19)H(21)F(3)O(2)S and C(24)H(19)F(3)OS, 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.