Alder Ene Reaction Hydro-Allyl Addition

The aza-ene reaction recently found application in the synthesis of imidazo[1,2-a]pyridine and imidazo[1,2,3- y][1,8]naphthyridine derivatives in the laboratory of Z.-T. Huang.The reaction of heterocyclic ketene aminals with enones such as MVK proceeded via an aza-ene addition, followed by intramolecular cyclization to afford the products. The aroyl-substituted heterocyclic ketene aminals (Ar=Ph, 2-furyl, 2-thienyl) underwent two subsequent aza-ene reactions when excess MVK was used. 

Ganem and co-workers accomplished the asymmetric totai synthesis of (-)-a-kainic acid using an enantioselective, metai-promoted ene cyclization. The chirai bis-oxazoiine-magnesium perchlorate system strongly favored the formation of the c/s-diastereomer in the cyclization. Enantiomerically pure kainic acid was synthesized from readily available starting materials on a 1-2 g scale in six steps in an overall yield of greater than 20%. 

The first total synthesis of (+)-arteannuin M was completed by L. Barriault et al. using a tandem oxy-Cope/transannular ene reaction as the key step to construct the bicyclic core of the natural product. The tandem reaction proceeded with high diastereo- and enantioselectivity. 

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