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

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 3R stereochemistry. The (1R,3R,4S) and (1R,3R,4R) stereoisomers were identical with the natural derivatives of the aphid insect pigments quinone A and quinone A′, while the (1S,3R,4S) and (1S,3R,4R) 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