Hypervalentiodine compounds are viable reagents for the oxidation of N,N-disubstitutedhydroxylamines to the corresponding nitrones, with IBX performing best. The procedure is very simple and user-friendly and affords the target compounds with high efficiency and regioselectivity, highlighting IBX as the reagent of choice for preparation of aldonitrones from nonsymmetric hydroxylamines. Evidence for
Total Synthesis of (+)-Decarbamoylsaxitoxin and (+)-Gonyautoxin 3
作者:Osamu Iwamoto、Kazuo Nagasawa
DOI:10.1021/ol1006696
日期:2010.5.7
Facile construction of the complex saxitoxin (STX) skeleton is carried out by using a novel, conformationally controlled, guanidine cyclization process that relies on the use of neighboring group participation. The utility of this methodology is verified by its employment in syntheses of both natural and unnatural STX derivatives.
Total Synthesis of (−)- and (+)-Decarbamoyloxysaxitoxin and (+)-Saxitoxin
作者:Osamu Iwamoto、Ryoko Shinohara、Kazuo Nagasawa
DOI:10.1002/asia.200800382
日期:2009.2.2
AbstractPlaying the sax: The enantioselective total syntheses of (−)‐ and (+)‐decarbamoyloxysaxitoxin (doSTX) and (+)‐saxitoxin (STX) are reported. A new methodology was developed for the synthesis of STXs, featuring discriminative reduction of the nitro group and NO bond in nitroisoxazolidine.magnified imageEnantioselective total syntheses of (−)‐ and (+)‐decarbamoyloxysaxitoxin (doSTX) and (+)‐saxitoxin (STX) were achieved. The characteristic spiro‐fused cyclic guanidine structure of STX was constructed by oxidation at the C4 position with IBX via an α‐iminium carbonyl intermediate and acid‐promoted cyclization of guanidine at the C5 position. A second‐generation methodology was developed for the synthesis of STX, featuring discriminative reduction of the nitro group and NO bond in nitroisoxazolidine. This approach provides efficient access to the key diamine intermediate for STXs.