Synthesis of Novel N-(R)-2-(1-Adamantyl)-1H-Benzimidazole-5(6)- Carboxamide, Carbohydrazide and 1,3,4-Oxadiazole Derivatives

A novel series of benzimidazole-5(6)-carboxamide 3a-g, carbohydrazide 5a-e and 1,3,4- oxadiazole 6a-g derivatives bearing adamantane moiety were synthesized. The synthesis of benzimidazole heterocycle was performed by direct condensation/cyclization reaction of 1- adamantanecarboxylic acid with methyl 3,4-diaminobenzoate in Trimethylsilyl Polyphosphate (PPSE). The obtained Methyl 2-(1-adamantyl)-1H-benzimidazole-5(6)-carboxylate was converted to desired carboxamide and carbohydrazide derivatives in two different ways. In the first case, the synthesized ester after hydrolysis was converted to an acid chloride and subsequently coupled with different aromatic and heterocycle amines to give carboxamide derivatives. In the second case, treatment with hydrazine hydrate gave corresponding 2-(1-adamantyl)-1H-benzimidazole-5(6)-carbohydrazide which was coupled with some acyl chlorides to give appropriate carbohydrazide derivatives and with some aromatic acids to give 1,3,4-oxadiazole derivatives.