2,6‐Dithiodecahydro‐1H,5H‐Diimidazo[4,5,‐b:4′,5′‐e]Pyrazine and related dioxo‐ and diimino‐decahydrodiimidazopyrazines

Abstract

AbstractThiourea condensed with 1,4‐diformyl‐2,3,5,6‐tetrahydroxypiperazine 2 in the presence of hydrochloric acid to give 2,6‐dithiodecahydro‐1 H,5H‐diimidazo[4,5,‐b:4′,5′‐e]pyrazine 5 isolated as the dihydrochloride salt. The salt 5. 2HCl was converted to the free base 5 by lithium hydroxide, to the dinitrate salt 5. 2HNO3 by silver nitrate, degraded to 2‐thio‐2,3,4,7‐tetrahydro‐1 H‐imidazo[4,5‐b]pyrazine 6 in a reaction with tert‐butyl amine, and converted to 4,8‐dihydro‐4,8‐dinitro‐1H,5H‐diimidazo[4,5‐b:4′,5′‐e]pyrazine‐2,6‐ disulfonic acid 9 by nitric acid (100%) at −40°C. Denitration of the dinitramine 9 to give 4,8‐dihydro‐1H,5H‐diimidazo[4,5‐b:4′,5′‐e]pyrazine 11 was brought about by methanolic hydrogen chloride in ether. In one run nitration without oxidation converted the salt 5 · 2HCl to the dinitrate salt of the 4,8‐dinitro derivative 10; treatment with triethyl amine liberated the free base 10 from the salt. Degradation of 2,6‐dioxo‐1,3,4,5,7,8‐hexanitrodecahydro‐1H,5H‐diimidazo[4,5‐b:4′,5′‐e]pyrazine 12 to 2‐oxo‐2,3‐dihydro‐1,3‐dinitro‐1H‐imidazo[4,5‐b] pyrazine 13 was brought about by hydrochloric acid. Treatment with lithium hydroxide also liberated 2,6‐dioxodecahydro‐1H,5H‐diimidazo [4,5‐b:4′,5′‐e]pyrazine 3 from its dihydrochloride salt. Attempts to liberate 2,6‐diiminodecahydro‐1H, 5H‐diimidazo[4,5‐b:4′,5′‐e]pyrazine 4 from its tetrahydrochloride salt led instead to intractable mixtures. The tetrahydrochloride salt 4 · 4HCl was converted to the dihydrochloride salt 4 · 2HCl in a reaction with tert‐butyl amine.