[2-CYCLOADDITION REACTION OF DIALKYLTHIOKETENES WITH CARBENES ISOMERIZATION OF THE RESULTING ALKYLIDENETHIIRANES(1])

Carbenes generates by metal-catalyzed decomposition of diazo compounds 2 undergo a smooth cycloaddition to the C=S bond of thioketenes 1; pr oducts 3 were characterized by spectroscopic means as well as an X-ray structural investigation of 3b. However, photolytic generation of dip henylcarbene from diphenylketene led to an isomeric alkylidenethiirane 4a in the reaction with di-tert-butylthioketene (1a). Analogously, al kylidenethiiranes 3a, b, d, g, h could be photoisomerized to isomers 4 a, b, d, g, h. The corresponding rearrangement of S-oxides 8 afforded isomers 9.