Stepwise acid-promoted double-Michael process: an alternative to Diels-Alder cycloadditions for hindered silyloxydiene-dienophile pairs.
The hindered diene 1 reacts with 3-methylcyclohexenone 6 catalyzed by triflimide to produce the Mukaiyama Michael product 7 (low-temperature quenching) or the [4+2] cycloadduct 8 (quenching at 0 degrees C). Reaction of the hindered diene 23 with 2-methylcyclohexenone 12 with 5:1 AlBr3:AlMe3 afforded a 71% yield of a 1.9:1 mixture of two cycloadducts. Hydrolysis of the major isomer gave the dione 27', a model for the BCD ring system of pentacyclic triterpenes. [reaction: see text].
Jung
Michael E
ME
Department of Chemistry and Biochemistry, University of California, Los Angeles, 405 Hilgard Avenue, Los Angeles, California 90095, USA. jung@chem.ucla.edu
Ho
David G
DG
D000466:Alkadienes / Q000737:chemistry*; D017607:Aluminum Compounds / Q000737:chemistry; D002384:Catalysis; D003500:Cyclization; D003512:Cyclohexanones / Q000737:chemistry*; D006868:Hydrolysis; D007094:Imides / Q000737:chemistry*; D015394:Molecular Structure; D013237:Stereoisomerism; D014315:Triterpenes / Q000138:chemical synthesis* / Q000737:chemistry
D000466:Alkadienes; D017607:Aluminum Compounds; D003512:Cyclohexanones; D007094:Imides; D014315:Triterpenes; C518058:triflimide