A study of nitrogen- and sulfur-containing heterocycles. 41. Synthesis and spatial structure of 3?-alkyl-4,7-dichloro-1,2-dioxooxazolidino[3,2-f]pyrido[2,3-b][1,4]thiazines

Abstract

The structure of the products of the chlorination of oxazolidino[3,2-f]pyrido-[2,3-b][1,4]-thiazines has been studied with the aid of spectral methods. It has been shown that the chlorine atom substitutes position 4 of the tricyclic system (in the thiazine ring). It has been established on the basis of PMR and 13C NMR spectra that in solution the compounds obtained exist in the form of mixtures of two diasteromers with the cis and trans orientations of the substituents at the C(3α) and C(4) carbon atoms of the tricyclic system in each case. The configurations of the diastereomers have been determined from the chemical shifts in the 13C NMR spectra and from the relaxation times in the PMR spectra. It has been shown that the isomer with the transoid arrangement of the substituents on the C(3α) and C(4) atoms of the tricyclic system, which are included in a thiazine ring present in the “half-chair” conformation, is energetically the more favorable.