Part 1. Permanganate promoted bi-directional oxidative cyclisation. Part 2. Permanganate-mediated asymmetric dihydroylation

Abstract

The central non-adjacent bis-THF core of the Annonaceous acetogenin cis-sylvaticin has been established via the permanganate promoted asymmetric bi-directional oxidative cyclisation of a tetraene. The tetraene was obtained in five facile steps from commercially available triene 4.27 in good overall yield. Permanganate promoted asymmetric bi-directional oxidative cyclisation inserted the eight new stereogenic centres in good d.r., thus providing rapid access to this advanced intermediate. Elaboration of the bis-THF core is described, illustrating the possibility of both a linear and bi-directional approach to cis-sylvaticin. An approach to the butenolide portion of cis-sylvaticin is also described. The key step involved asymmetric alkynyl addition to butenolide-aldehyde 3.6 and proceeded with good levels of diastereoselectivity. The permanganate-mediated asymmetric dihydroxylation of enones has been demonstrated in the presence of a chiral quaternary ammonium salt. Dihydroxylation of a variety of enone substrates produced the corresponding diols with good levels of enantioselectivity (50-80% ee). The reaction is clean and fast, producing the corresponding benzoic acid as the main by-product.

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