STEREOSPECIFIC INTRAMOLECULAR MICHAEL ADDITION TO (-)-CARVONE BASED ON TEMPORARY SULFUR CONNECTION

An acetic acid residue (CH2CO2Me) was stereoselectively attached to (- )-carvone (7) to give 5R)-(5-isopropenyl-2-methyl-3-oxocyclohexyl)acet ic acid methyl ester (21) in a process involving the following stages: i) addition of ClSCH2CO2Me to the isopropenyl group of 7 to give, aft er oxidation, ,4-methyl-5-oxocyclohex-3-enyl)propane-2-sulfonyl] aceti c acid methyl ester (18); ii) intramolecular Michael addition of 18 to afford loromethyl-4,8-dimethyl-3,3,7-trioxo-3-thiabicyclo [3.3.1]nona ne-2-carboxylic acid methyl ester (20); iii) disconnection of the acet ic acid moiety by a tandem reductive elimination involving sulfur extr usion and restoration of the isopropenyl group (20 --> 21). (C) 1998 E lsevier Science Ltd. All rights reserved.