Hygrophorone B12, a new antifungal constituent from the fruiting bodies of Hygrophorus abieticola, has been isolated and subsquently synthesized in enantiomerically pure form. The total synthesis includes a Sharpless asymmetric dihydroxylation protocol as the stereodifferentiating step, followed by two diastereoselective aldol‐type reactions. The approach allows the unambiguous control of all three stereogenic centres, and, furthermore, unequivocal determination of the relative and absolute configuration of antibiotic hygrophorones B for the first time.

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Based on naturally occurring hygrophorones, racemic di‐ and mono‐hydroxylated cyclopentenones bearing an aliphatic side chain have been produced in short synthetic sequences starting from furfuryl aldehyde. For the series of dihydroxylated trans‐configured derivatives, an Achmatowicz‐rearrangement and a Caddick‐ring contraction were employed, and for the series of trans‐configured mono‐hydroxylated derivatives a Piancatelli‐rearrangement. All final products showed good to excellent fungicidal activities against the plant pathogens B. cinerea, S. tritici and P. infestans.