2H-Pyran-2-ones from Trichoderma viride and Trichoderma asperellum

Volatiles emitted by the soil fungi Trichoderma viride 272 and Trichoderma asperellum 328 were collected by using the closed loop stripping analysis (CLSA) headspace technique, and the obtained extracts were analysed by GC/MS. Several alkyl- and alkenyl-2H-pyran-2-ones, including known compounds 6-pentyl-2H-pyran-2-one and (E)-6-(pent-1-en-1-yl)-2H-pyran-2-one, and the new derivatives (E)-6-(pent-2-en-1-yl)-2H-pyran-2-one, 6-propyl-2H-pyran-2-one, and 6-heptyl-2H-pyran-2-one were found. The alkenyl derivative (E)-6-(hept-1-en-1-yl)-2H-pyran-2-one, previously tentatively identified from a marine Botrytis by MS analysis, was also detected. All alkenyl pyrones were synthesised by using a reported Stille coupling followed by lactonisation, whereas the alkylated pyrones were obtained through a reported synthetic approach by radical bromination of 5-alkylpent-2-en-5-olides and dehydrobromination. Because the yields in both cases were not satisfactory and fell a long way short of the yields reported for similar compounds, all compounds were synthesised again using a gold-catalysed coupling of terminal alkynes with propiolic acid recently developed by Schreiber and co-workers, giving high yields in all cases. A comparison of the synthetic methods is given.