Chemistry of amidines. Part 3. Analysis of conformation about the N′-pyridyl bond in N′-(2-pyridyl)formamidines

Abstract

A conformational analysis of a series of N,N-dimethyl-N′-(2-pyridyl)formamidines and their conjugate acids using the 1H NMR nuclear Overhauser effect shows that they exist preferentially in the conformation in which the pyridine and the imino nitrogen lone pairs are anti. For compounds having electron-donating substituents the syn conformation becomes important on protonation.