Glucopyranosyl radical synthesis

Radical reduction of 1-nitro-C-glycosyl compounds. In 1983, Vasella and co-workers125 reported a stereoselective method for the synthesis of a-C-mannopyranosyl compounds by reduction of 1-nitro-C-mannopyranosyl derivatives with Bu3SnH in the presence of a,a -azoisobutyronitrile (AIBN) radical initiator. These reactions involve the formation of anomeric centered radicals. Thus, in the case of d-manno configuration as in 140, the 1,2-cts-C-pyranosyl compound 145 was obtained in 84% yield. The intermediate pyranosyl radicals 143 prefer a-attack by the tin hydride. Thus for D-glucopyranosyl derivatives, the corresponding l,2-tra x-C-pyranosyl compound 144 is obtained preferentially (Scheme 47). 

AT-Acyl Derivatives. — O-Protected 2-deoxy-2-trichloroacetamido-D-glucopyranosyl trichloroacetimidates, e.g. 54, have been used in the synthesis of -linked disaccharides with some success (see Chapter 3). The products could be converted into the corresponding 2-acetamido-derivatives by radical dechlorination (BuaSnH, AIBN). The 2-trichIoromethyl-oxazoline derivative 55, formed from 3,4,6-tri-0-acetyl-2-deoxy-2-trichloroacetamido-D-glucosyI acetate (on reaction... 

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