4.8 Article

Mild Homologation of Esters through Continuous Flow Chloroacetate Claisen Reactions

期刊

ANGEWANDTE CHEMIE-INTERNATIONAL EDITION
卷 57, 期 52, 页码 17249-17253

出版社

WILEY-V C H VERLAG GMBH
DOI: 10.1002/anie.201810158

关键词

chloroketones; homologation; microreactors

资金

  1. Deutsche Forschungsgemeinschaft [SFB 749]
  2. German Academic Scholarship Foundation

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The selective chloromethylenation of functionalized esters using chloroacetic acid (CA) and LiHMDS (HMDS = hexamethyldisilazide) in a continuous-flow setup is reported. This Claisen homologation is for the first time extended to bis-chloromethylenation using dichloroacetic acid (DCA), thus giving access to under-explored alpha,alpha'-bis-chloroketones. The use of flow conditions enables efficient generation and reaction of the unstable chloroacetate dianion intermediates, leading to unprecedented mild and scalable reaction conditions at an economical reagent stoichiometry (-10 degrees C, <1 min, 1.0-2.4 equiv dianion). The clean reaction profiles allow subsequent use of the unpurified crude products, which is demonstrated in the synthesis of various heterocycles of broad interest. Furthermore, we report a novel, catalyst-free substitution of the obtained monochloro ketone products with (hetero)aryl zinc enolates to give valuable 1,4-diketones.

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