Palladium-Mediated Ring Closure Reactions. Facile Syntheses of Enantiopure Bicyclic and Tricyclic Alkenones

(R)-Carvone was used as a chiral building block. Regio- and stereoselective alkylations at C6 and C2 of (R)-carvone and (R)-5-isopropyl-2-methyl-2-cyclohexenone [derived from the hydrogenation of (R)-carvone] followed by palladium-mediated ring closures afforded various enantiopure bicyclic and tricyclic alkenones. Hence, cyclization of (5S,6S)-2,6-dimethyl-6-(cis-3-iodo-2-propenyl)-5-isopropenyl-2-cyclohexenone (3) gave (4aS,5S,8aS)-1,4,4a,5,8,8a-hexahydro-5-(methoxycarbonylmethyl)-2,5,8a-trimethylnaphthalen-1-one (7) as the major product, cyclization of (5S,6S)-2,6-dimethyl-6-(cis-3-iodo-2-propenyl)-5-isopropyl-2-cyclohexenone (22) produced (1S,5R,6S)-1,5-dimethyl-6-isopropyltricyclo[3.3.1.02,8]-3-nonen-9-one (23), and cyclization of (2R,5S,6S)-2,6-dimethyl-2-(cis-3-iodo-2-propenyl)-5-isopropenyl-3-cyclohexen-1-one (25) afforded (3aR,6S,7aR)-6,7a-dimethyl-5-isopropenyl-3a,6,7,7a-tetrahydro-1H-inden-7-one (26). A 1,2-rearrangement reaction of bromide 16 gave hexahydro-1H-benzocycloheptene 17.