Synthesis of Dihydropyridines and Pyridines from Imines and Alkynes via C−H Activation

A convenient one-pot C−H alkenylation/electrocyclization/aromatization sequence has been
developed for the synthesis of highly substituted pyridine derivatives from alkynes and α,β-unsaturated
N-benzyl aldimines and ketimines that proceeds through dihydropyridine intermediates. A new class of
ligands for C−H activation was developed, providing broader scope for the alkenylation step than could be
achieved with previously reported ligands. Substantial information was obtained about the mechanism of
the reaction. This included the isolation of a C−H activated complex and its structure determination by
X-ray analysis; in addition, kinetic simulations using the Copasi software were employed to determine rate
constants for this transformation, implicating facile C−H oxidative addition and slow reductive elimination
steps.