Conformational analysis and inversion process in some perhydrodipyrido[1/2- b;1′/2′/-e]-1,4,2,5-dioxadiazines

The stereoselectivity in the cyclodimerization of several six-membered cyclic nitrones has been investigated. The configurational/conformational analysis of the dimers (i.e. perhydrodipyrido[1, 2-b;1, 2, -e]-1, 4, 2, 5-dioxadiazinesj has been carried out by NMR spectroscopy. The NMR spectra of the dimers at lower temperatures indicated the presence of either a single or two invertomer(s). The nitrogen inversion barriers are determined using complete line-shape analysis. The invertomer ratios have been used to estimate the relative energies associated with the cis and trans ring fusion in these tricycles. A mechanistic rationale for the observed stereochemistry of the dimerization process has been presented.