2-Methyl-6-nitroaniline → 2,3-Diaminotoluene

The 5,6-dihydro-N,N-dipropyl-4H-imidazo(4,5,1-j)quinolin-5-amines of the invention, compounds of Formula I where D is nitrogen, A is CH, n is 0 and D and A are joined by a double bond, may be prepared as illustrated in Scheme 2 for the preparation of compound 6. Catalytic hydrogenation of 2-methyl-6-nitroaniline (XVI) using a palladium catalyst afforded 3-methyl-1,2-benzenediamine (XVIII) which was heated with formic acid to give 4-methylbenzimidazole (XVIII). This was heated in dioxane with di-t-butyl dicarbonate and the t-butyl 4-methylbenzimidazole-1-carboxylate (XIXa, R is OC(CH3)3) thus obtained was brominated with N-bromosuccinimide in carbon tetrachloride to give t-butyl 4-(bromomethyl)benzimidazole-1-carboxylate (XXa). Alkylation of XXa with the potassium salt of diethyl (dipropylamino)-malonate (VIb) in refluxing THF afforded XXIa which was hydrolyzed to XXII using sodium ethoxide in ethanol containing limited amounts of water. Compound XXII was reduced to the alcohol XXIII using lithium aluminum hydride. When XXIII was treated with carbon tetrabromide and triphenylphosphine in methylene chloride compound 6 was obtained directly.