Enamide complexation, regioselectivity

Figure 2. Regioselectivity in enamide complexation phosphorus-31 NMR spectra, MeOH, 25° C.

The low ee-values obtained with simple unsaturated acids as compared to the enamides of dehydroamino acid derivatives show that the oxygen atoms of the amide is a key to complex formation with the metal center. Knowles also proposed a quadrant model that has been adapted for many reactions [5, 22]. The mechanism of the reaction has been investigated, and it is known that the addition of the substrate to the metal is regioselective and that competing catalytic cycles can occur [5, 10, 22, 25, 27, 30-46]. 

Interestingly, Lam has described a synthesis of enamides via rhodium-catalyzed carbozincation of ynamides [175]. When applied to dialkenylzinc compounds, this reaction leads to the regio- and stereoselective formation of 1-amidodienes 224 (Scheme 87). The regioselectivity of the reaction was explained by the possible formation of a chelated complex 223. 

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