α-<i>N-</i>Acetylmannosamine (ManNAc) Synthesis via Rhodium(II)-Catalyzed Oxidative Cyclization of Glucal 3-Carbamates
作者:Rena Bodner、Bridget K. Marcellino、Alexandra Severino、Abigail L. Smenton、Christian M. Rojas
DOI:10.1021/jo0500129
日期:2005.5.1
Glucal 3-carbamates 1 and 7 underwent oxidative cyclization with iodobenzene diacetate or iodosobenzene in the presence of Rh-2(OAc)(4), providing mannosamine 2-N,3-O-oxazolidinones. With iodosobenzene, incorporation of 4-penten-1-ol provided a readily separable anomeric mixture of n-pentenyl glycosides, with the anomers exhibiting pronounced differences in reactivity as glycosyl donors. N-acylation of the sugar oxazolidinones led to a-selective glycosyl donors for the elaboration of various 2-mannosamine frameworks. Alternatively, the anomeric n-pentenyl glycosides of N-Cbz 2-mannosamine oxazolidinones were converted separately to oxazolidinone-opened derivatives 28 alpha and 28 beta. These served as stereoconvergent glycosyl donors, and the a-linked products were readily advanced to a variety of N-acetylmannosamine (ManNAc) frameworks, using an intramolecular O -> N acetyl transfer as the final step.