Rhodium(III)-catalyzed vinylic C-H activation: a direct route toward pyridinium salts.

A synthetic method for highly substituted pyridinium salts from the multicomponent reaction of vinyl ketones/aldehydes, amines, and alkynes using a rhodium catalyst is demonstrated. The catalytic reaction proceeds via an in situ generated imine-assisted Rh(III)-catalyzed vinylic C-H activation.

Rh(III) -catalyzed C-H activation: a versatile route towards various polycyclic pyridinium salts.

An efficient and convenient method for the synthesis of highly substituted polycyclic pyridinium salts from the reaction of various 2-aryl-pyridines and 2-aryl-sp(2) -nitrogen-atom-containing heterocycles with alkynes through rhodium(III)-catalyzed CH activation and annulation under an O2 atmosphere is described. A possible mechanism that involves the chelation-assisted CH activation of the 2-aryl-pyridine substrate, insertion of the alkyne, and reductive elimination is proposed. This mechanism was supported by the isolation of a five-membered rhodacycle (I').

A convenient synthesis of quinolizinium salts through Rh(III) or Ru(II)-catalyzed C-H bond activation of 2-alkenylpyridines.

An efficient synthesis of quinolizinium salts from 2-vinylpyridines and alkynes via Rh(III) or Ru(II)-catalyzed C-H activation and annulation reaction is described. A possible mechanism involving pyridine assisted vinylic ortho-C-H activation, alkyne insertion and reductive elimination is proposed.