Pigments of fungi. Part 41. Synthesis of (S)-(+)- and (±)-dermolactone; stereochemistry of dermolactone from the Australian fungus Dermocybe sanguinea(Wulf. ex Fr.) Wünsche sensu Cleland

Abstract

(S)-(+)-Dermolactone 3 has been synthesised in monochiral form beginning with ethyl (S)-lactate, the tetracyclic nucleus being assembled by way of a regiospecific cycloaddition between the known chloronaphthoquinone 15 and the novel, highly functionalised chiral butadiene derivative 5. Isochiral dermolactone 3+4 is prepared in the same way from (±)-5. Dermolactone, as it occurs naturally, is shown by ¹H NMR shift experiments on the corresponding permethyl ethers 25 and 27, using [Eu(+)-(hfc)₃], to consist of an anisochiral mixture of the (S)-(+)- and (R)-(–)-enantiomers 3 and 4, respectively, in which the former predominates in the ratio of 1.8:1 (28.6% ee).