or Ph3P - CCl4] of triketides bearing optically active functional groups to the corresponding γ-pyrones provided determination of the absolute configurations of ilikonapyrone and peroniatriols I and II isolated from the marine molluscs Onchidium verruculatum and Peronia peronii.
Neighboring-groupparticipation of an acyl protecting group efficiently promotes the Bronsted acid-catalyzed dehydrative cyclization of 1,3,5-triketones to gamma-pyrones, whereas a bulky silyloxy group in the beta-position retards the cyclization. This reaction provides an efficient synthetic route for a common intermediate for the synthesis of gamma-pyrone-containing bioactive natural products.
The synthesis of vallartanone B, a γ-pyrone-containing polypropionate from the marine mollusc Siphonaria maura, is described. A γ-pyrone moiety, which was constructed by PPh3-CCl4 cyclization of a β-triketone, and a C1-C6 segment were joined by a Sn(OTf)2 aldol reaction and converted to vallartanone B. This synthesis allows for revision of the stereochemistry at C8. A conformational analysis was performed