Organic syntheses via transition metal complexes, CV - Regiocontrol of annelation of cyclopentene-1-thiones and cyclopenten-1-ones to alkenes with the aid of (1-alkynyl)carbene complexes (M = Cr, W)

Bicyclic olefins containing a 1-oxy-3-thiocyclopentadiene unit were obtaine d with high regioselectivity from [2-(cyclo-alk-1-enyl)-1-alkynyl]carbene c omplexes 1a-d and thiols 2a-c under mild conditions. If the reaction was pe rformed in a protic solvent like ethanol, the produced allylthiocyclopentad ienes 5 spontaneously underwent a thio Claisen rearrangement to give cyclop entene-1-thione complexes 3 in 62-72% yields. In nonprotic solvents, additi onal cyclopentene-1-thione complexes 6 and 7 were obtained as a result of t he incorporation of two and three allylthiol units, respectively, Arylthiol etrahydroindene complexes 12b and c could be isolated in 76-79% yields. The corresponding tetrahydropentalene derivative 12a was unstable, but could b e trapped by [2+2] cycloaddition of (1-alkynyl)carbene complex la to give a stable (cyclobutenyl)carbene complex 15. Hydrolysis of compounds 12a-c aff orded cyclopenten-1-ones 13a-c.