Michael addition stereoelectronic factors

Irie and co-workers (37) have recently observed that the double Michael reaction of dimethyl acetone dicarboxylate on dienone 104 gave the cis decal-in product 106. This result indicates that intermediate 105 underwent a stereoelectronically controlled internal Michael addition to give 106. Without stereoelectronic control in the Michael reaction, there is no apparent reason to prevent the formation of the trans isomer 107. However, if this factor is taken into consideration, examination of molecular models indicates that it seems impossible to obtain isomer 107. 

The stereochemistry of nucleophilic 1,4-additions to enones (Michael-type additions) is controlled by stereoelectronic factors. In the absence of compelling steric effects, the nucleophile approaches the [3-carbon of the enone antipamllel to the neighboring (y) pseudoaxial substituent (circled H in the example below). 

Stereoselection can also occur in the intramolecular Michael addition. Factors other than those operative in the acyclic additions may influence the stereochemistry. In particular, certain stereoelectronic preferences are important in cyclizations that are not considerations in acyclic examples. In this respect, enamine and enolate cyclizations often exhibit similar behavior/... 

Factors controlling the stereochemistry of conjugate additions are not well understood. Mixtures of isomers are often produced, but generally one isomer predominates. Both steric and electronic factors play a role. ° Generally, Michael-type additions have late and hence productlike—and chairlike— transition states. In the example shown below, for stereoelectronic reasons antiparallel attack by the nucleophilic CH3 is favored over parallel attack. 

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