First Total Synthesis of (±)-Melinonine-E and (±)-Strychnoxanthine Using a Radical Cyclization Process as the Core Ring-Forming Step
作者:Josefina Quirante、Carmen Escolano、Alma Merino、Josep Bonjoch
DOI:10.1021/jo971148c
日期:1998.2.1
The first total synthesis of (+/-)-melinonine-E and (+/-)-strychnoxanthine is described. The key common step for the synthesis of both alkaloids is the elaboration of the 8-azabicyclo[3.3.1]nonane nucleus (D and E rings) by a radical carbocyclization, using an alpha-carbamoyldichloromethyl radical as a donor. The closure of the C ring by a Bischler-Napieralski cyclization, followed by an epimerization process to gain the axial nitrile 20, and appropriate reduction transformations afforded pentacyclic alcohol 23. This alcohol was converted into either (+/-)-melinonine-E (1) or (+/-)-strychnoxanthine (2) by means of a palladium black dehydrogenation of the C ring or a SeO2 oxidation of the corresponding acetate 25, respectively.