Ammonium salts, alkyl with amide bases

With respect to the substrate scope, ketones are the most efficient nucleophiles although the intermolecular reaction works also well for esters, amides and Weinreb amides (Fig. 2.7). Regarding the Michael acceptor, enones are the best electrophiles with a wide range of substituents tolerated (alkyl, aryl and heteroaryl ketones). a,p-Unsaturated esters, in the case of the intermolecular cyclopropanation, and a,p-unsaturated diimides for the intramolecular reaction, extends the substrate scope of the process (Fig. 2.7). A transition state model for the intramolecular cyclopropanation reaction has been proposed as depicted in Scheme 2.38 for catalyst 65 [106d]. In this model the ammonium salt adopts a conformation that gives the Z-enolate of the nucleophile on deprotonation with the base. The intramolecular conjugate addition of the enolate then takes place through a boat-type transition state. 

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