Enantioselective Solvent-Free Synthesis of 3-Alkyl-3-hydroxy-2-oxoindoles Catalyzed by Binam-Prolinamides
作者:Abraham Bañn-Caballero、Jesús Flores-Ferrándiz、Gabriela Guillena、Carmen Nájera
DOI:10.3390/molecules200712901
日期:——
BINAM-prolinamides are very efficient catalyst for the synthesis of non-protected and N-benzyl isatin derivatives by using an aldol reaction between ketones and isatins under solvent-free conditions. The results in terms of diastereo- and enantioselectivities are good, up to 99% de and 97% ee, and higher to those previously reported in the literature under similar reaction conditions. A high variation of the results is observed depending on the structure of the isatin and the ketone used in the process. While 90% of ee and 97% ee, respectively, is obtained by using (Ra)-BINAM-l-(bis)prolinamide as catalyst in the addition of cyclohexanone and α-methoxyacetone to free isatin, 90% ee is achieved for the reaction between N-benzyl isatin and acetone using N-tosyl BINAM-l-prolinamide as catalyst. This reaction is also carried out using a silica BINAM-l-prolinamide supported catalyst under solvent-free conditions, which can be reused up to five times giving similar results.
BINAM-prolinamides 是一种非常高效的催化剂,可通过在无溶剂条件下使用酮和异靛的醛缩反应合成非保护性和 N-苄基异靛衍生物。在立体选择性和对映选择性方面的结果良好,达到高达 99% 的 diastereomer excess (de) 和 97% 的 enantiomeric excess (ee),且高于文献中在类似反应条件下所报告的结果。根据所使用的异靛和酮的结构,结果呈现出较大的变化。当使用 (Ra)-BINAM-l-(bis)prolinamide 作为催化剂,将环己酮和 α-甲氧基丙酮添加到自由异靛时,分别可获得 90% 和 97% 的 ee;而在 N-苄基异靛与丙酮的反应中,使用 N-tosyl BINAM-l-prolinamide 作为催化剂可获得 90% 的 ee。该反应还可以在无溶剂条件下使用硅基 BINAM-l-prolinamide 支持催化剂进行,该催化剂可重复使用多达五次,并产生类似的结果。