Chiral synthons from carvone. Part 50. Enantiospecific approaches to both enantiomers of bicyclo[4.3.0]nonane-3,8-dione derivatives

Abstract

Enantiospecific synthesis of both enantiomeric forms of bicyclo[4.3.0]nonane-3,8-dione derivatives has been described starting from (R)-carvone employing two different cyclopentannulation methodologies. Thus, in the first methodology, carveol (5) was converted into tricyclic ketone 4 employing a Claisen rearrangement and intramolecular diazo ketone cyclopropanation reactions. Degradation of the isopropenyl group followed by cyclopropane cleavage and cuprate addition generated the dione (−)-12a. Whereas, a Wacker mediated cyclopentannulation of (R)-carvone via the dione 15 furnished the enone 17. Functional group manipulation including the degradation of isopropenyl group transformed the enone 17 into the dione (+)-12a, which on regioselective ketalisation generated the ketoketal (+)-2.