Pigments of Fungi. XV. An Efficient, Unambiguous Route to Unsymmetrically Substituted Dibenzyl Acyloins and Their Use in the Synthesis of Fungus Pigments of the Pulvinone and Grevillin Types

Dibenzyl acyloins including those bearing unsymmetrically disposed aryl residues are assembled in high yield by reaction between the O-trimethylsilyl ethers of arylacetaldehyde cyanohydrins and benzyl Grignard reagents. These acyloins are deprotonated with lithium diisopropylamide to afford alcoholate-enolate dianions which can be made to react with carbonyldiimidazole and with oxalyldiimidazole, respectively, to ultimately afford fungus pigments of the pulvinone and grevillin types.