Active-methylene compounds base-catalyzed Michael additions

Fig. 13.67. Mechanism of the base-catalyzed Michael addition of active-methylene compounds (top) and of ketones (bottom), respectively. Subst refers to a substituent, and EWG stands for electron-with-drawing group.

Michael condensations are catalyzed by alkaU alkoxides, tertiary amines, and quaternary bases and salts. Active methylene compounds and aUphatic nitro compounds add to form P-substituted propionates. These addition reactions are frequendy reversible at high temperatures. Exceptions are the tertiary nitro adducts which are converted to olefins at elevated temperatures (24). 

Michael condensation reactions (base-catalyzed addition of active methylene compounds to activated unsaturated systems) were reported in 1887." This reaction has been used to prepare... 

The asymmetric Michael addition of active methylene or methyne compounds to electron deficient olefins, particularly a,P-unsaturated carbonyl compounds, represents a fundamental and useful approach to construct functionalized carbon frameworks [51]. The first successful, phase-transfer-catalyzed process was based on the use of well-designed chiral crown ethers 69 and 70 as catalyst. In the presence of 69, P-keto ester 65 was added to methyl vinyl ketone (MVK) in moderate yield but with virtually complete stereochemical control. In much the same way, crown 70 was shown to be effective for the reaction of methyl 2-phenylpropionate 67 with methyl acrylate, affording the Michael adduct 68 in 80% yield and 83% ee (Scheme 11.15) [52]. 

---