Palladium-mediated ring closure reactions. Facile syntheses of enantiopurebicyclic 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-cyc lohexenone [derived from the hydrogenation of (R)-carvone] followed by pall adium-mediated ring closures afforded various enantiopure bicyclic and tric yclic 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,5,8,8 a-hexahydro-5-(methoxycarbonylmethyl)-2,5,8a-trimethylnapthalen-1-one (7) a s the major product, cyclization of (5S,6S)-2,6-dimethyl-6-(cis-3-iodo-2-pr openyl)-5-isopropyl-2-cyclohex (22) produced (1S,5R,6S)-1,5-dimethyl-6-isop ropyltricyclo[3.3.1.0(2,8)]-3-nonen-9-one (23), and cyclization of (2R,5S,6 S)-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-tetrahydr o-1H-inden-7-one (26). A 1,2-rearrangement reaction of bromide 16 gave hexa hydro-1H-benzocycloheptene 17. (C) 2000 Elsevier Science Ltd. All rights re served.