Compounds with Bridgehead Nitrogen 52 -NMR Spectra and Stereochemistry of the 2-Alkylperhydroimidazolopyridines

Article abstract of DOI:10.1002/mrc.1260250808

In contrast to perhydro-oxazolo<3,4-a>pyridine and perhydrothiazolo<3,4-a>pyridine, which adopt equilibria in CDCl3 solution at room temperature containing ca 70percent trans-fused conformers in equilibria with O- or S-inside cis-fused conformers, 2-alkylperhydroimidazolo<3,4-a>pyridines are found to adopt equilibria containing >98percent trans-fused conformers.Comparison of NMR parameters of 2-methylperhydroimidazolo<3,4-a>pyridine with those of the two isomers of 1,2-dimethylperhydroimidazolo<3,4-a>pyridine indicates an equilibrium for the former compound between the two trans-fused conformers, with ca 83percent of that conformation containing a transarrangement of nitrogen lone pairs of electrons.These observations are explained in terms of the generalized anomeric effect.KEY WORDS Perhydroimidazolo<3,4-a>pyridine Conformational equilibria 1H and 13C NMR