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

Bera, Kalisankar ; Namboothiri, Irishi N. N. (2015) Quinine-Derived Thiourea and Squaramide Catalyzed Conjugate Addition of α-Nitrophosphonates to Enones: Asymmetric Synthesis of Quaternary α-Aminophosphonates Journal of Organic Chemistry, 80 (3). pp. 1402-1413. ISSN 0022-3263

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Official URL: http://doi.org/10.1021/jo502332r

Related URL: http://dx.doi.org/10.1021/jo502332r

Abstract

Conjugate addition of α-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 α-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 α-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 π-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 α-nitrophosphonates could be easily transformed to synthetically and biologically useful quaternary α-aminophosphonates and other multifunctional molecules.

Item Type:Article
Source:Copyright of this article belongs to American Chemical Society.
Keywords:Organophosphorus Compounds; Catalysts; Aromatic Compounds; Stereoselectivity; Enones.
ID Code:121396
Deposited On:15 Jul 2021 12:07
Last Modified:15 Jul 2021 12:07

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