Chalcogen-Bond Catalysis: Telluronium-Catalyzed [4+2]- Cyclocondensation of (in situ Generated) Aryl Imines with Alkenes

In the chalcogen series, tellurium species exhibit the strongest chalcogen bonding (ChB) interaction with electron-rich atom. This property explains the renewed interested toward tellurium-based derivatives and their use in different applications, such as organocatalysis. In this context, the catalytic activity of telluronium salts in the Povarov reaction is presented herein. Different dienophiles, as well as imines of variable electronic nature, efficiently react in the presence of catalytic amount of either diarylmethyltelluronium or triaryltelluronium salts. Both catalysts could also readily perform the three-component Povarov reaction starting from aldehyde, aniline and dihydrofuran. The reactivity of telluroniums towards imines and aldehydes was confirmed in the solid state by the ability of Te atom to interact through ChB with the oxygen carbonyl of acetone, and in solution with significant shift variations of the imine proton and of the tellurium atom in H-1 and Te-125 NMR spectroscopy. For the most active telluronium catalysts bearing CF3 groups, association constants (K) with N-phenyl phenylmethanimine in the range 22-38 M-1 were measured in dichloromethane.

Automated summary

Tellurium species in the chalcogen series exhibit strong chalcogen bonding (ChB) interaction with electron-rich atoms, which has sparked renewed interest in tellurium-based derivatives for various applications. In this study, the catalytic activity of telluronium salts in the Povarov reaction is presented. Different dienophiles and imines efficiently react in the presence of diarylmethyltelluronium or triaryltelluronium salts as catalysts, and these catalysts can also perform the three-component Povarov reaction. The reactivity of telluroniums towards imines and aldehydes was confirmed through solid state and solution-state spectroscopy.