Reduction and reductive coupling of imines by Sm(II)-based reagents

The reductive coupling of aldimines and ketimines by a series of Sm(II)-based reagents (SmI2, SmI2–HMPA, SmBr2, Sm{N[Si(CH3)3]2}2, and SmI2/triethylamine/water) were examined. In general, aldimines and ketimines were efficiently reduced or coupled using reductants that are more powerful than SmI2, and the use of Sm{N[Si(CH3)3]2}2 led to higher diastereoselectivities in reductive coupling reactions. Surprisingly, only the combination of SmI2/triethylamine/water was capable of reducing and coupling para-substituted benzaldimines and coupling ketimines.