Enantioselective Synthesis of Quaternary α-Amino Acids via <scp>l</scp>-<i>tert</i>-Leucine-Derived Squaramide-Catalyzed Conjugate Addition of α-Nitrocarboxylates to Enones
作者:Kalisankar Bera、Nishikant S. Satam、Irishi N. N. Namboothiri
DOI:10.1021/acs.joc.6b00543
日期:2016.7.1
Enantioselective Michael addition of tertiary α-nitroesters to β-unsubstituted vinyl ketones has been carried out in the presence of an l-tert-leucine-derived squaramide as organocatalyst. The products, quaternary α-nitroesters, were formed in excellent yield and moderate to good ee’s in most cases. Scale-up of the reaction and synthetic applications of the products, including transformation to representative
Chiral bifunctional squaramide catalyzed asymmetric tandem Michael-cyclization reaction: efficient synthesis of optically active 2-amino-4H-chromene-3-carbonitrile derivatives
We have developed an efficient bifunctional squaramide catalyst for the asymmetric tandem Michael addition-cyclization of malononitrile to functionalized nitroolefins. This organocatalytic asymmetric reaction provides convenient and valuable access to highly functionalized 2-amino-4H-chromene derivatives, which possess important biological activities, in good yields with moderate to high enantioselectivities (up to 95% ee). (C) 2013 Elsevier Ltd. All rights reserved.