Chiral Brønsted Base-Promoted Nitroalkane Alkylation: Enantioselective Synthesis of <i>sec</i>-Alkyl-3-Substituted Indoles
作者:Mark C. Dobish、Jeffrey N. Johnston
DOI:10.1021/ol1025712
日期:2010.12.17
A Brønsted base-catalyzed reaction of nitroalkanes with alkyl electrophiles provides indole heterocycles substituted at C3 bearing a sec-alkyl group with good enantioselectivity (up to 90% ee). Denitration by hydrogenolysis provides a product with equally high ee. An indolenine intermediate is implicated in the addition step, and surprisingly, water cosolvent was found to have a beneficial effect in
硝基烷烃与烷基亲电试剂的布朗斯台德碱催化反应提供了在 C3 处取代的吲哚杂环,带有一个具有良好对映选择性(高达 90% ee)的仲烷基。通过氢解脱硝提供具有同样高 ee 的产品。在添加步骤中涉及吲哚中间体,令人惊讶的是,发现水共溶剂在该步骤中具有有益作用,导致使用 PBAM(一种双(脒)手性非外消旋碱)消除/对映选择性添加的一锅法。
Solvent-Free Non-Covalent Organocatalysis: Enantioselective Addition of Nitroalkanes to Alkylideneindolenines as a Flexible Gateway to Optically Active Tryptamine Derivatives
A catalytic asymmetric addition of nitroalkanes to alkylideneindolenines, generated in situ from arylsulfonylindoles, is presented. Despite the weakness of the non‐covalent H‐bond interactions between catalyst and substrates, the performance of the bifunctional organocatalyst used was found to be essentially unaffected by the polarity of the reaction medium. Nitroalkanes, mostly used in nearly stoichiometric
The catalytic asymmetric phase-transfer cyanation of alkylideneindolenines, generated in situ from sulfonylalkylindoles, was developed. In the presence of sodium cyanide and a catalytic amount of chiral 1,2,3-triazolium salt, a series of sulfonylalkylindoles can be transformed into the corresponding chiral 3-sec-alkylindoles with good-to-high levels of efficiency and enantioselectivity.
ABSTRACT A catalyst-freethree-componentreaction of indoles, carbonyls, and arenesulfinic acids performed at room temperature provides direct access to biologically important 3-(1-arylsulfonylalkyl)indoles. This process features mild conditions, low cost, broad substrate scope, and high yields, and mechanistically bis(indolyl)methanes were identified as the key intermediates. GRAPHICAL ABSTRACT