Radikalische Cyclisierung von Dienen, VI. Substratkontrollierte asymmetrische Synthese von (3aS,6aR)-(+)-3,3a,6,6a-Tetrahydro-2H-cyclopenta[b]furan-2-on

Radical-Type Cyclization of Dienes, VI. – Substrate-Controlled Asymmetric Synthesis of (3aS,6aR)-(+)-3,3a,6,6a-Tetrahydro-2H-cyclopenta[b]furan-2-one (R)-(−)-Carvone (1) was converted via straightforward reactions into 10-hydroxycarvone (4) which was cyclized to 5 via the mercury-mediated free-radical method. Periodate cleavage of 5 yields the bicyclic dione 6. Regio- and stereoselective reduction of 6 with lithium tri(tert-butyloxy)hydridoaluminate results in 7 (80% yield). 7 was directly converted into γ-lactone 8 via Baeyer-Villiger oxidation. Saponification of 8 to 9, mesylation of 9 to 10 followed by elimination of methanesulfonic acid yield enantiomerically pure (3aS,6aR)-(+)-3,3a,6,6a-Tetrahydro-2H-cyclopenta[b]furan-2-one (11). The synthesis can be carried out with readily available, and economical, (S)-(+)-carvone to yield ent-11.