An Efficient Conjugate Addition of Dialkyl Phosphite to Electron-Deficient Olefins: The Use of a Nucleophilic organocatalyst to Form a Strong Base

摘要

The formation of a zwitterionic species between electron-deficient olefins and tertiary amine or phosphine is a pivotal and the starting point for the Morita-Baylis-Hillman (MBH) reaction and Rauhut-Currier (RC) reaction. A subsequent 1,2-addition of the zwitterion I, which was generated from methyl acrylate as an example, to aldehyde and a proton movement furnished the Morita-Baylis-Hillman adduct, whereas a conjugate addition to electron-deficient olefins is the Rauhut-Currier reaction, as shown in Scheme 1. Basically, the zwitterion is an ester enolate and could act as a base.34 In this respect, White and Baizer reported a phosphine-catalyzed conjugate addition of 2-nitropropane to various electron-deficient olefins, as also shown in Scheme 1. Toste and co-workers reported a phosphine-catalyzed conjugate addition of alcohol or water to electron-deficient olefins. Later, Pedduri and Williamson have applied the concept to make tetrahydrofurans. Vallribera and co-workers also reported the conjugate addition of p-dicarbonyl compounds to electron-deficient olefins. The mechanism of the conjugate additions likely involves the zwitterion I behaving as a base to deprotonate the nitroalkane, alcohol, water and β-dicarbonyl; the nitronate, alkoxide, hydroxide or the enolate of β-dicarbonyl then undergoes the following conjugate additions to electron-deficient olefins. Recently, Tian and co-workers have developed an efficient alternative way to Henry reaction involving a deprotonation of a nitroalkane with the zwitterionic ester enolate to form a nitronate and a subsequent reaction with aldehyde.