Enolonium species/iodo(III)enolates of carbonyl compounds have been suggested to be intermediates in a wide variety of hypervalent iodine induced chemical transformations of ketones, including α-C-O, α-C-N, α-C-C, and α-carbon-halide bond formation, but they have never been characterized. We report that these elusive umpoled enolates may be made as discrete species that are stable for several minutes at -78 °C, and report the first spectroscopic identification of such species. It is shown that enolonium species are direct intermediates in C-O, C-N, C-Cl, and C-C bond forming reactions. Our results open up chemical space for designing a variety of new transformations. We showcase the ability of enolonium species to react with prenyl, crotyl, cinnamyl, and allyl silanes with absolute regioselectivity in up to 92 % yield.
Enolonium species/iodo(III)enolates of carbonyl compounds have been suggested to be intermediates in a wide variety of hypervalent iodine induced chemical transformations of ketones, including α‐C−O, α‐C−N, α‐C−C, and α‐carbon–halide bond formation, but they have never been characterized. We report that these elusive umpoled enolates may be made as discrete species that are stable for several minutes at −78 °C, and report the first spectroscopic identification of such species. It is shown that enolonium species are direct intermediates in C−O, C−N, C−Cl, and C−C bond forming reactions. Our results open up chemical space for designing a variety of new transformations. We showcase the ability of enolonium species to react with prenyl, crotyl, cinnamyl, and allyl silanes with absolute regioselectivity in up to 92 % yield.
Abstractα‐Hydrogen‐substituted nitroxyl radicals are of considerable interest as catalysts for oxidation and polymerization, but are usually inherently unstable. We report herein the catalytic activity of a new family of stable iso‐azaphenalene (IAPNO) α‐hydrogen nitroxyl radicals in the copper/bipyridine/N‐methylimidazole co‐catalyzed aerobic oxidation of alcohols. The nitroxyl radical Mes/TIPSO‐IAPNO (TIPSO=triisopropyloxy, IAPNO=isoazaphenalene N‐oxyl) displays higher activity than TEMPO in the oxidation of benzylic and allylic alcohols. Alkyl, benzyl, allyl, and propargyl alcohols are oxidized with yields up to 96 %. The readily prepared nitroxyl catalysts are recovered in 75–90 % yield after purification of the reaction mixture and are recycled.
Umpolung alkylation of Evans' auxiliary substituted β-ketoimides affords the diastereomerically pure products in yields ranging from 40 to 80%. The reaction itself proceeds with diastereoselectivities between 3 : 1 and 18 : 1. Dialkylzinc serves as the nucleophile and umpolung of the β-keto-imide enolate is achieved by the action of Koser's reagent.
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