Guindon, Yvan; Guérin, Brigitte; Rancourt, Jean; Chabot, Catherine; Mackintosh, Nicole et Ogilvie, W.W.
(1996).
« Lewis acids in diastereoselective processes involving acyclic radicals ».
Pure and Applied Chemistry, 68(1), pp. 89-96.
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Résumé
The radical reductions and allylations of a series of alpha-halo-P-alkoxy esters under bidentate chelation-controlled conditions are reported and compared with the analogous reactions under non-chelating conditions. The addition of Lewis acids is shown to give excellent selectivity for the syn products in the case of reduction, and the anti products in the case of allylation. In some cases, ratios greater than 1OO:l are obtained. The reactions require initiation with EbB and can be inhibited by m- and p-dinitrobenzene, which imply a radical-based mechanism. Iodides, bromides and phenyl selenides are all suitable substrates. Investigations also provide a rationale for the large excess of MgBr2.OEt2 which is apparently required in these reactions. Competition experiments provide a more detailed explanation of substrate reactivity.
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