Asymmetric diastereoselective syntheses of the aphid insect pigment derivatives quinone A and quinone A′

Abstract

Commercially available ( R)-lactate has been used to provide the chiral source for the asymmetric diastereoselective syntheses of all four stereoisomers of 3,4-dihydro-4,7,9-trihydroxy-1,3-dimethylnaphtho[2,3- c]pyran-5,10-quinone based on 3 R stereochemistry. The (1 R,3 R,4 S) and (1 R,3 R,4 R) stereoisomers were identical with the natural derivatives of the aphid insect pigments quinone A and quinone A′, while the (1 S,3 R,4 S) and (1 S,3 R,4 R) stereoisomers were found to be the enantiomers of two hitherto unreported naturally derived quinones from alternative aphid insect sources. A key-step is the titanium tetraisopropoxide-induced intramolecular diastereoselective cyclization of meta-hydroxybenzyl protected lactaldehydes to afford benzo[ c]pyran-4,5-diols.