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Quinine-Derived Thiourea and Squaramide Catalyzed Conjugate Addition of alpha-Nitrophosphonates to Enones: Asymmetric Synthesis of Quaternary alpha-Aminophosphonates

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Title Quinine-Derived Thiourea and Squaramide Catalyzed Conjugate Addition of alpha-Nitrophosphonates to Enones: Asymmetric Synthesis of Quaternary alpha-Aminophosphonates
 
Creator BERA, K
NAMBOOTHIRI, INN
 
Subject ENANTIOSELECTIVE MICHAEL-ADDITION
PHOSPHONIC ACID-DERIVATIVES
CHIRAL SULFINYL AUXILIARY
STEREOSELECTIVE-SYNTHESIS
AMINO PHOSPHONATES
DIASTEREOSELECTIVE SYNTHESIS
ISOTHIOCYANATO PHOSPHONATES
ANTITUMOR-ACTIVITY
ALDOL REACTION
HYDROPHOSPHONYLATION
 
Description Conjugate addition of a-nitrophosphonates to enones was carried out in the presence of two sets of organocatalysts, viz. a quinine-thiourea and a quinine-squaramide. The quinine-thiourea provided the products possessing an a-quaternary chiral center in high enantioselectivities only in the case of electron rich enones. On the other hand, the quinine-squaramide was more efficient in that a wide variety of electron rich and electron poor enones underwent Michael addition of nitrophosphonates to afford the quaternary a-nitrophosphonates in excellent yields and enantioselectivities. The hydrogen bonding donor ability of the bifunctional catalyst, as shown in the proposed transition states, appears primarily responsible for the observed selectivity. However, a favorable p-stacking between the aryl groups of thiourea/squaramide and aryl vinyl ketone also appeared favorable. The reaction was amenable to scale up, and the enantioenriched quaternary a-nitrophosphonates could be easily transformed to synthetically and biologically useful quaternary a-aminophosphonates and other multifunctional molecules.
 
Publisher AMER CHEMICAL SOC
 
Date 2016-01-15T06:27:38Z
2016-01-15T06:27:38Z
2015
 
Type Article
 
Identifier JOURNAL OF ORGANIC CHEMISTRY, 80(3)1402-1413
0022-3263
http://dx.doi.org/10.1021/jo502332r
http://dspace.library.iitb.ac.in/jspui/handle/100/17931
 
Language en