Highly Stereoselective (3+2) Cycloadditions of Levoglucosenone (LGO) with the In Situ-Generated Thiocarbonyl S-Methanides (Thiocarbonyl Ylides) Derived from Aromatic and Cycloaliphatic Thioketones

The in situ-generated thiocarbonyl S-methanides derived from cycloaliphatic thioketones undergo (3+2) cycloaddition onto the C=C bond of levoglucosenone yielding anticipated, polycyclic tetrahydrothiophene derivatives in a regio- and stereoselective manner. The cycloaddition process occurred stereoselectively via the less hindered exo-face approach; exo-diastereoisomers were formed in all studied reactions. Some of the obtained crystalline (3+2) cycloadducts were studied by the monocrystal X-ray diffraction analysis, which unambiguously confirmed the postulated structure. Stable (3+2) cycloadducts were isolated in good yields (50–80%).