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 Sour ce for the asymmetric diastereoselective syntheses of all four stereoisomer s of 3,4-dihydro-4,7,9-trihydroxy-1,3-dimethylnaphtho [2,3-c]pyran-5,10-qui none based on 3R stereochemistry. The (1R,3R,4S) Lind (1R,3R,4R) stereoisom ers were identical with the natural derivatives of the aphid insect pigment s quinone A and quinone A', while the (1S,3R,4S) and (IS,3R,4R) stereoisome rs were found to be the enantiomers of two hitherto unreported naturally de rived quinones from alternative aphid insect sources. A key-step is the tit anium tetraisopropoxide-induced intramolecular diastereoselective cyclizati on of meta-hydroxybenzyl protected lactaldehydes to afford benzo[c]pyran-4, 5-diols. (C) 2001 Elsevier Science Ltd. All rights reserved.