Synthesis of fused cyanopyrroles and spirocyclopropanes via addition of N-ylides to chalconimines.

Addition of N-ylides derived from DABCO to chalconimines takes place through a Michael addition-cyclization pathway to afford fused cyanopyrroles and/or spirocyclopropanes. The product profile depends heavily on the nature of chalconimines. While 6-membered cyclic chalconimines provide a mixture of pyrrole and spirocyclopropane, 5-membered chalconimines furnish exclusively spirocyclopropane. Cyclopropane was the only product in the case of a representative open chain chalconimine as well. On the other hand, chalcones provide only spirocyclopropanes which is in contrast to the previously reported reactivity of enones. The complementary nature of the reactivity of the tetralone derived chalcone and its corresponding imine in providing spirocyclopropane and pyrrole, respectively, has also been demonstrated.

Transition-metal-catalyzed hydrogen-transfer annulations: access to heterocyclic scaffolds.

The ability of hydrogen-transfer transition-metal catalysts, which enable increasingly rapid access to important structural scaffolds from simple starting materials, has led to a plethora of research efforts on the construction of heterocyclic scaffolds. Transition-metal-catalyzed hydrogen-transfer annulations are environmentally benign and highly atom-economical as they release of water and hydrogen as by-product and utilize renewable feedstock alcohols as starting materials. Recent advances in this field with respect to the annulations of alcohols with various nucleophilic partners, thus leading to the formation of heterocyclic scaffolds, are highlighted herein.