PHOTOLYSIS OF ALPHA-DIAZOCYCLOPENTANONES - RING CONTRACTION TO FUNCTIONALIZED CYCLOBUTANES AND SYNTHESIS OF JUNIONONE, GRANDISOL AND PLANOCOCCYL ACETATE

Photolysis of diazoketone 19 in methanol furnished the cyclobutane carboxylate 20. Photolysis in aqueous sodium bicarbonate-THF afforded the acid 21 in better yield. Reduction of the ester followed by oxidation and a subsequent Wittig reaction furnished ± junionone (3). Photolysis of the diazoketone 24 resulted in a 1:1 mixture of cyclobutane carboxylates 25. Treatment of the corresponding carboxylic acids with hydriodic acid furnished the bicyclic lactone 27, a known precursor of grandisol (1). The diazoketone 28, on photolysis yielded a mixture of cyclobutane carboxylates 29 and 30. Conversion of the trans acid 31 to a methyl ketone followed by oxidative functionalisation of the phenyl group gave the keto ester 36 which was isomerised under acid catalysis to 37, which in optically active form had been a precursor to (-) grandisol. Photolysis of diazoketone 38 afforded the cyclobutane carboxylates 39 and 40 in 2:1 proportion. The corresponding mixture of acids on treatment with methyl lithium and subsequent acetylation furnished the keto acetates 43 and 44, resulting in a formal synthesis of planococcyl acetate (4). © 1990.