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  • Title: Generation of acyloxyketenes from unstable mesoionic 1,3-dioxolium-4-olates and their reaction with ketenophiles to give [2 + 2] cycloadducts.
    Author: Hamaguchi M, Tomida N, Iyama Y, Oshima T.
    Journal: J Org Chem; 2006 Jul 07; 71(14):5162-70. PubMed ID: 16808502.
    Abstract:
    Fast ring opening of mesoionic 1,3-dioxolium-4-olates, generated by Rh(2)(OAc)(4)-catalyzed decomposition of phenyldiazoacetic anhydride derivatives, to acyloxyphenylketenes was demonstrated by trapping the ketenes with several ketenophiles. Reactions of phenyldiazoacetic anhydride derivatives with several ketenophiles such as dihydrofuran, carbodiimides, and imines were carried out. No 1,3-dipolar cycloadducts of the latter with 1,3-dioxolium-4-olates were observed. Instead, only their [2 + 2]-cycloadducts with the acyloxyketenes generated by ring-opening of the initially formed 1,3-dioxolium-4-olates were isolated. In the reaction with cyclopentadiene, 1,3-dipolar cycloadducts with 1,3-dioxolium-4-olates were formed as main products along with the [2 + 2]-ketene adduct. PM3 calculation of heats of formation of 2,5-diphenyl-1,3-dioxolium-4-olate and the corresponding benzoyloxyphenylketene indicates that the ring-opened acyloxyketenes are ca. 9 kcal/mol more stable than the corresponding 1,3-dioxolium-4-olates.
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