Regioselectivity in the ring opening of 2-phenyl-1,3-dioxan-2-yl radicals derived from cyclic benzylidene acetals and comparison with deoxygenation of a carbohydrate diol via its cyclic thionocarbonate

✍ Scribed by Brian P Roberts; Teika M Smits

• Publisher: Elsevier Science
• Year: 2001
• Tongue: French
• Weight: 107 KB
• Volume: 42
• Category: Article
• ISSN: 0040-4039
• DOI: 10.1016/s0040-4039(01)00540-8

✦ Synopsis

Ring-opening b-scission of monocyclic 2-phenyl-1,3-dioxan-2-yl radicals gives preferentially the more stabilised alkyl radical. However, analogous bicyclic radicals derived from two 4,6-O-benzylidene glucopyranosides afford primary radicals in preference to secondary radicals, a result that can be rationalised with the aid of DFT calculations. The report by Barton and Subramanian, that the opposite regioselectivity results from the tin hydride mediated reductive ring-opening of a corresponding glucosidic thionocarbonate, is shown to be in error.