Radical cyclisation strategies to bridged systems. Regioselective construction of chiral bicyclo [2.2.2] and [3.2.1] octanes via 6-exo trig and 5-exo trig radical cyclisation reactions
作者:A. Srikrishna、P. Hemmalini
DOI:10.1016/s0040-4020(01)85623-4
日期:1992.1
Radical cyclisation reaction of the bromoenones and , obtained from (R)-phenyl carvone , gave a mixture of bicyclo [2.2.2] and [3.2.1] octanones via competitive 6-exo trig and 5-exo trig modes. On the other hand, radical cyclisation reaction of the alcohol furnished the bicyclo[3.2.1]-octanol as the major cyclised product, where as the alcohol furnished the bicyclo[2.2.2]octanol as the major cyclised
Chiral synthons from carvone. 9. 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
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 nBu3SnH and AIBN, even in the presence of a large excess of a radicophile. On the other hand, bromoenone 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.