ABSTRACT
In this paper, a new cycloaddition between α,ß-unsaturated aldehydes and coumalates realized under dienamine activation has been described. The reaction proceeds regioselectively with the distal double bond of the dienamine system acting as electron-rich dienophile. It leads to the formation of biologically relevant [2.2.2]-bicyclic lactones. Their functionalization potential has been confirmed in selected, diastereoselective transformations.
ABSTRACT
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 1.60â Å, although this is also observed in related structures. In the same structure, weak inter-molecular C-Hâ¯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-Hâ¯π inter-actions link the mol-ecules into sheets parallel to the (010) plane.
ABSTRACT
Selected hetaryl and aryl thioketones react with acetylenecarboxylates under thermal conditions in the presence of LiClO4 or, alternatively, under high-pressure conditions (5 kbar) at room temperature yielding thiopyran derivatives. The hetero-Diels-Alder reaction occurs in a chemo- and regioselective manner. The initially formed [4 + 2] cycloadducts rearrange via a 1,3-hydrogen shift sequence to give the final products. The latter were smoothly oxidized by treatment with mCPBA to the corresponding sulfones.
