Synthesis and stereochemistry of 2-pyrone derivatives related to some fungal metabolites

Abstract

Some stereochemistry of 'asperlin' (1) and related fungal metabolites containing a 5,6-dihydro-2-pyrone moiety, has been deduced through correlation of nmr and ord parameters with those of reference compounds derived from carbohydrates of known stereochemistry. The reference compounds are 4,6-di-O-acetyl-2,3-dideoxy-D-threo- and -D-erythro-hex-2-enono-1,5-lactones obtained by modification of D-galactal and D-glucal, respectively, and the D-enantiomer of 1, synthesized in a multistep sequence from D-galactose. It is shown that the 5,6-substituents of the pyrone ring of 1 have the L-threo configuration and also that the exocyclic epoxypropyl moiety is trans.