A new short synthetic approach to chlorocyclopentenones related to cryptosporiopsin via a ring expansion strategy: first synthesis of a fungitoxic metabolite from Sporormia affinis

A metabolite of the coprophilous fungus, Sporormia affinis, 2-trans-allyl-5-chloro-1-hydroxy-4-oxo-2-cyclopentene-1-carboxylic acid methyl ester, 2, was synthesized in racemic form, by an eight-step sequence, in 11% overall yield. Departing from previous ring-contraction strategies for synthesis of chlorocyclopentenones in the cryptosporiopsin series, the key step in the new synthesis was ring expansion of a substituted cyclobutanone, the product of [2+2] cycloaddition of dichloroketene with methyl 2-trimethylsilyloxyhex-2-enoate.Key words: Sporormia affinis, cryptosporiopsin, chlorocyclopentenone, dichloroketene, [2+2] cycloaddition, ring expansion, selenium dioxide.