119. 2-Alkynylcyclopent-2-enols from 2-alkynylcyclohex-2-enones via 1-alkynyl-7-oxabicyclo[4.1.0]heptan-2-ones

Article abstract of DOI:10.1002/hlca.19960790515

2-Alkynylcyclohex-2-enones 1a-c and 2a-c react with H₂O₂/NaOH in MeOH to afford 1-alkynyl-7-oxabicyclo[4.1.0]heptan-2-ones 3a-c and 4a-c, respectively. The 3-unsubstituted bicyclic epoxy ketones 3a, 3b, and 4a, 4b react further with H₂O₂/NaOH, undergoing ring contraction and (formal) decarbonylation to give 2-alkynylcyclopent-2-enols 5a, 5b, and 6a, 6b, respectively. Epoxy ketones 3 are also obtained under neutral conditions on irradiation (λ = 350 nm) of cyclohexenones 1 in air-saturated benzene solution. Similarly, under neutral conditions oxo-cycloalkenecarbonitriles 8 react (thermally) with H₂O₂ in MeCN to give the oxabicyclic carbonitriles 9.