A Diels–Alder/Retro‐Diels–Alder Approach for the Enantioselective Synthesis of Microbial Butenolides

Several volatile lactones have been identified from the endophytic fungus Geniculosporium sp. isolated from the rockrose Cistus monspeliensis, commonly known as Montpelier cistus. The fungal volatiles were collected from agar‐plate cultures by using a closed‐loop stripping apparatus and the headspace extracts were analysed by GC–MS. Structures for these lactones were proposed from their mass spectral data. The suggested structures were verified by synthesis of reference compounds through a Diels–Alder/retro‐Diels–Alder approach. This synthetic method was also successfully applied in the synthesis of butenolides that are signalling molecules from streptomycetes. For the enantioselective synthesis of these butenolides a modified route including an enantioselective Diels–Alder reaction was used.