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The scope of the reaction of 2-aminobenzimidazole, aldehydes and diethyl malonate in the presence of silica sulfuric acid/ethylene glycol was investigated. The reaction gave two unexpected products, 2-hydroxyethyl 3-hydroxy-4-aryl-2-oxo-tetrahydropyrimidobenzimidazole-3-carboxylates  2  and 4-aryl-hydropyrimido[1,2- a ]- benzimidazol-2(1 H )-ones  3  without isolation of the expected ethyl 4-aryl-2-oxo-1,2,3,4-1,2,3,4-tetrahydropyrimido[1,2- a ]benzimidazole-3-carboxylates  1 . NMR spectroscopic data and X-Ray analysis were used for assignment and confirmation the structures of the unexpected products. 2-Hydroxyethyl carboxylate derivatives  2  may be obtained  via  formation of  1  as intermediates, which were subjected to trans-esterification by ethylene glycol and oxidation of the proton on pyrimidine ring at position-3 to afford products  2 . The unexpected products  3  may be obtained  via  formation of compounds  1  that was subjected to deesterification followed by decarboxylation to afford compounds  3 .

Synthesis of Novel Diastereomer Pyrimido[1,2- a ]Benzimidazoles by Using Silica Sulfuric Acid/Ethylene Glycol