Base-catalyzed cascade 1,6-sulfur-Michael/Henry reaction of trifluoromethyl-substituted styrylisoxazoles: Diastereoselective synthesis of tetrahydrothiophenes with a trifluoromethylated quaternary center

Chemo- and regioselective [3 + 2]-cyclo-additions of thio-carbonyl ylides: crystal structures of trans-8-benzoyl-1,1,3,3-tetra-methyl-7-tri-fluoro-methyl-5-thia-spiro-[3.4]octan-2-one and trans-3-benzoyl-2,2-diphenyl-4-(tri-fluoro-meth-yl)tetra-hydro-thio-phene

The title compounds, C19H21F3O2S and C24H19F3OS, were prepared via chemo- and regioselective [3 + 2]-cyclo-additions of the respective thio-carbonyl ylides (thio-carbonyl S-methanides), generated in situ, with (E)-4,4,4-tri-fluoro-1-phenyl-but-2-en-1-one. The thio-phene ring in the crystal structure of each compound has an envelope conformation. The largest differences between the two mol-ecular structures is in the bond lengths about the quaternary C atom of the thio-phene ring; in the spiro-cyclic structure, the C-C bonds to the spiro C atom in the cyclo-butane ring are around 1.60 Å, although this is also observed in related structures. In the same structure, weak inter-molecular C-H⋯X (X = S, O) inter-actions link the mol-ecules into extended ribbons running parallel to the [001] direction. In the other structure, weak C-H⋯π inter-actions link the mol-ecules into sheets parallel to the (010) plane.