The conformational analysis of saturated heterocycles. Part 90. Syntheses and conformational analysis of 1,2,4-trimethyl- and 1,2,3,4-tetramethyl-1,2,4-triazacyclohexanes

Abstract

The first syntheses are described of saturated 1,2,4-triazacyclohexanes. The 1,2,4-trimethyl derivative exists predominantly in the eae conformation: at lower temperatures minor amounts of eee⇌eea(ca. 10%) and then aee(ca. 5%) are frozen out. Kinetic and thermodynamic parameters are obtained from variable-temperature ¹³C n.m.r. spectra. ‘Passing’(ΔG_c^‡ca. 12 kcal mol^–1) and ‘non-passing’(ΔG_c^‡ca. 8 kcal mol^–1) nitrogen-inversion barriers are clearly differentiated.