Bicyclic olefins containing a 1-oxy-3-thiocyclopentadiene unit were obtained with high regioselectivity from [2-(cycloalk-1-enyl)-1-alkynyl]carbene complexes 1a−d and thiols 2a−c under mild conditions. If the reaction was performed in a proticsolvent like ethanol, the produced allylthiocyclopentadienes 5 spontaneously underwent a thio Claisen rearrangement to give cyclopentene-1-thione complexes 3