1999 reduction, hydrogenation

reduction, hydrogenationO 0220

07 - 063The Use of Lewis Acids in Radical Chemistry. Chelation-ControlledRadical Reductions of Substituted α-Bromo-β-alkoxy Esters andChelation-Controlled Radical Addition Reactions. — Scope andlimitations of the chelation-controlled radical reduction of α-bromo-β-alkoxyesters are investigated. The reaction tolerates a wide variety of substitutionsand is unaffected by the relative configuration of the substrate with exceptionof steric demanding groups at position 3 [cf. reactions of (Ib) and (IVb)].Changes to the alkoxy and ester functions indicate a bidentate chelate to beinvolved in the reaction. In the presence of MgBr2·OEt2 the reduction requiresinitiation and is inhibited by 1,3-dinitrobenzene, thus demonstrating typicalbehavior of radical chain reactions. Further support for this mechanism isprovided by radical addition to α,β-unsaturated esters (not shown; some yieldsnot given). — (GUINDON, Y.; RANCOURT, J.; J. Org. Chem. 63 (1998)19, 6554-6565; Inst. Rech. Clin. Montreal, Montreal, Que. H2W 1R7, Can.; EN)

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