AbstractThe samarium diiodide reduction of glycosyl pyridyl sulfones bearing a silicon‐tethered unsaturated group at the C2–OH position leads to the stereo‐specific synthesis of 1,2‐cis‐C‐glycosides in good yield after desilylation. These reactions proceed via an anomeric radical with subsequent 5‐exo cyclization. Unlike the corresponding glycosyl phenyl sulfones, the pyridyl derivatives react instantaneously with samarium diiodide and do not require a cosolvent such as hexamethylphosphoramide (HMPA). Under these reaction conditions radical cyclization precedes the second reduction step. Examples of 5‐exo‐trig and ‐dig ring closures are given. The synthetic utility of this method was demonstrated by a short synthesis of methyl C‐isomaltoside.
Nickel-catalyzed preparation of stereodefined allylic alcohols using silicon-tethered ynals
作者:Mario Lozanov、John Montgomery
DOI:10.1016/s0040-4039(01)00461-0
日期:2001.5
The nickel-catalyzed cyclization of silicon-tethered ynals is reported. The silicon heterocycles obtained may be converted into allylicalcohols that possess a stereodefined alkene unit via a cleavage process that involves stereospecific protodesilylation of the vinyl silane functionality.