Stereoselective Alkylation of α,β-Unsaturated Imines via C−H Bond Activation

The stereoselective alkylation of α,β-unsaturated imines via C−H activation followed by imine hydrolysis produces tri- and tetrasubstituted α,β-unsaturated aldehydes. In the presence of a rhodium catalyst, α,β-unsaturated N-benzyl imines derived from methacrolein, crotonaldehyde, and tiglic aldehyde undergo directed C−H activation at the β-position and react with terminal alkenes and alkynes to form the tri- and tetrasubstituted α,β-unsaturated imines with very high stereoselectivity. Hydrolysis to provide α,β-unsaturated aldehydes can be performed under carefully controlled conditions that maintain the stereochemistry of the β-alkylated imine products. Alternatively, for β-alkylation products of the N-benzyl imine of methacrolein, hydrolysis can be performed under conditions that provide complete isomerization to the E isomer.