Total Synthesis of Mappicine Ketone (Nothapodytine B) by Means of Sulfur-Directed 5-<i>exo</i>-Selective Aryl Radical Cyclization onto Enamides
作者:Issei Kato、Masayuki Higashimoto、Osamu Tamura、Hiroyuki Ishibashi
DOI:10.1021/jo030177m
日期:2003.10.1
Enamides 5, on treatment with Bu3SnH-AIBN, underwent aryl radical cyclization in a 5-exo manner to give 1-[bis(phenylthio)methyl]dihydroisoindoles 6, which were partially desulfurized with Bu3SnH-AIBN to give 1-mono(phenylthio)methyl congeners 7. Formation of 6 from 5 may be explained by the presence of two phenylthio groups at the terminus of the N-vinylic bond of 5, since enamide Sa having no phenylthio group underwent aryl radical cyclization in a 6-endo manner. Compound 7d (R = CF3) was transformed into sulfoxide 16, which was treated with (CF3CO)(2)O and then with 10% NaOH to give a model compound 20 of mappicine ketone (MPK) (1) through aldol condensation of aldehyde 18. An attempt to synthesize MPK using this method with sulfoxide 28 prepared from 25, however, was unsuccessful, and, instead, photochemical cyclization of enamide 38 prepared from 25 furnished MPK.