Abstract
A facile method for the preparation of N1‐ (1a–6a) and N3‐alkylated (1b–6b) 4‐azabenzimidazole derivatives is presented. Both isomers were obtained by alkylation of 4‐azabenzimidazole. The isomers were separated, and the preferred formation of the N1‐alkylated derivatives (1a–6a) was observed. The C2‐proton in the alkylated benzimidazoles can be exchanged for an iodine atom by treatment with methyl lithium and iodine, leading to N‐alkylated 2‐iodo‐4‐azabenzimidazoles 7a,b and 8a. 2,2^′^‐Bis(4‐azabenzimidazole) derivatives 9a,b and 10a were isolated as by‐products of the proton–halogen exchange. Treatment of the N1‐ or N3‐methyl‐4‐azabenzimidazoles 1a,b with methyl lithium and N‐chlorosuccinimide as a chlorine source proceeded to give 2‐chloro‐4‐azabenzimidazoles 11a,b without formation of the coupling products, but the yield of 2‐chloro‐1‐methyl‐4‐azabenzimidazole 11a is low (9%) whereas 2‐chloro‐3‐methyl‐4‐azabenzimidazole 11b has been obtained in reasonable yield (49%). The reaction of 3‐butyl‐2‐iodo‐4‐azabenzimidazole 7b with [IrCl~2~Cp*]~2~ gave the iridium complex 12, where 3‐butyl‐2‐iodo‐4‐azabenzimidazole is coordinating to the metal center via the N1 atom. The reaction of the N1‐alkylated 4‐azabenzimidazole with chloroacetone gave the corresponding 1‐alkyl‐3‐(2‐oxopropyl)‐4‐azabenzimidazolium chlorides 13–17 in good yields. The chloride counterion was exchanged for a tetrafluoroborate anion for two derivatives leading to compounds 18 and 19. Carbene complexes were obtained by treatment of 1‐butyl‐3‐(2‐oxopropyl)‐4‐azabenzimidazolium chloride 15 with silver oxide, followed by transmetalation with [AuCl(tht)] or [IrCl~2~Cp*]~2~ leading to the gold(I) (20) and iridium(III) complexes (21) with 1‐butyl‐3‐(2‐oxopropyl)‐4‐azabenzimidazolin‐2‐ylidene ligand. Removal of the 2‐oxopropyl protecting group by treatment with silica gel proceeded in the case of the iridium complex to give complex 22, possessing an NH,NR‐stabilized carbene ligand, while it failed for the gold(I) complex. © 2011 Wiley Periodicals, Inc. Heteroatom Chem 22:476–490, 2011; View this article online at wileyonlinelibrary.com. DOI 10.1002/hc.20711