Sterically crowded heterocycles. XII. Atropisomerism of (1-aryl-3,5-diphenyl-1H-pyrrol-2-yl)(phenyl)methanones

Some 1-(2-substituted phenyl)- and 1-(1-naphthyl)-2,4,6-triphenylpyridinium perchlorates were treated with potassium hexacyano ferrate(III)-potassium hydroxide reagent to give the title pyrroles. Restricted rotation around th e C-N bond in the products is demonstrated by NMR experiments with homochir al shift reagents, by semiempirical PM3 calculations as well as using their atropodiastereoselective and enantioselective transformations. Racemisatio n barriers for the (R)-2-(N-methyl-N-phenylcarbamoyl) derivative were estim ated from NMR and polarimetric measurements.