A convenient synthesis of glycals employing in-situ generated Cp2TiCl
摘要:
Reductive elimination of acetylated glycosyl bromides to the corresponding glycal is easily achieved by mixing the bromide with Cp2TiCl2 and Mn in THF, and hence does not require the separate preparation of Cp2TiCl using glove-box techniques. (C) 1999 Elsevier Science Ltd. All rights reserved.
1,2-cis-C-glycoside synthesis by samarium diiodide-promoted radical cyclizations
摘要:
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.