4-substituted tandem vicinal difunctionalization

Simple substitution at the a-carbon of the enoate substrate also does not appear to have much effect on the course of the reaction methyl acrylate and methyl methacrylate both function well as substrates in the reaction sequence and isolated yields of the products are similar.100 In certain sterically demanding reaction sequences, a-substitution does reduce the chemical yields of the products but the presence of an a-substituent appears to be of greater importance than the particular identity of the substituent.101 As with ketones, enoate substrates are activated towards tandem vicinal difunctionalization when electron-withdrawing a-substituents are present.102-104... 

Enoate 3-substitution and 3-disubstitution cause a decrease in the rate of the initial conjugate addition step of the reaction sequence that is directly related to the steric bulk of the substituent.103,105 Equation (24) provides a representative case in the a-alkylation of enoates by means of conjugate amination-enol-ate alkylation followed by dehydroamination.106 When 3-substitution results in stereoisomeric ( )- and (Z)-alkenoate substrates, tandem difunctionalization typically proceeds with greater facility for ( )-isomers.64103 Obviously, when the double bond of the ester is part of a medium-sized ring, an ( )-alke-noate geometry is mandated in such cases, tandem vicinal difunctionalization proceeds with uniformly excellent results (equation 25).25... 

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