Radical Annulation Strategy to Chiral Pupukeanones: Total Synthesis of (+)-10-exo-(1-Naphthyl)pupukean-9-one and (+)-10-exo-(1-Naphthyl)-5-epipupukean-9-ones

Article abstract of DOI:10.1021/jo00061a026

Intramolecular alkylation reaction of the bromoenone 12, obtained from S-carvone in three steps, furnished the bicyclo<2.2.2>octenone 13.Contrary to the anticipated radical annulation reaction, the bicyclic bromides 14 and 15, obtained from the enone 13, generated exclusively the cyclopropane product 18 via a 3-exo-trig radical cyclization on reaction with n-Bu3SnH and AIBN, even in the presence of a large excess of a radicophile.On the other hand, bromenone 24, synthesized from R-carvone via S-naphthylcarvone 21, underwent radical annulation reaction in the presence of radicophiles to furnish the isotwistanes 25-28 in a regio- and stereospecific manner.Hydrogenation of the olefin 34, obtained from the diketone 27 via a regiospecific Wittig reaction, furnished the naphthyl-5-epipupukean-9-one 33, whereas stereoselective hydrogenation of the enone 36, prepared from the keto ester 25 via a Grignard reaction and dehydration sequence, generated the naphthylpupukeanone 32.