Synthesis of Alkylidenecyclopentenones and Dialkylidenecyclopentenones via the Coupling of Propargylic Alcohol and 2-Alkyne-1,4-diol Derivatives with Cyclopropylcarbene–Chromium Complexes

The coupling of propargylic alcohols and their derivatives with cyclopropylcarbene–chromium complexes has been investigated. The coupling reaction leads to alkylidenecyclopentenones or alkoxyalkyl-cyclopentenones, depending on the leaving group ability of the propargyl substituent. A mechanism involving formation of a cyclopentadienone, followed by reduction and β-elimination is proposed. Coupling of cyclopropylcarbene complexes with 2-alkyne-1,4-diol derivatives leads to dialkylidenecyclopentenone derivatives via a double elimination process.