An environmentally benign and efficient method has been developed for the synthesis of a series of benzo[4,5]imidazo[1,2-a]pyrimido[4,5-d]pyrimidin-4(1H)-one derivatives in aqueous media under catalyst-free conditions by simply combining 2-aminobenzimidazole, aldehyde, and cyanoacetamide. The advantages of this method are that it is catalyst-free, has an easy workup, provides excellent yields, and uses water as the solvent which is considered to be relatively environmentally benign.

A straightforward and general method has been developed for the synthesis of benzo[4,5]imidazo[1,2-a]pyrimidine and [1,2,4]triazolo[1,5-a]pyrimidine derivatives by simply combining 2-aminobenzimidazole or 3-amino-1,2,4-triazole, aldehyde, and β-dicarbonyl compound in the presence of a catalytic amount of thiamine hydrochloride (VB1). The advantages of this method are the use of an inexpensive and readily available catalyst, easy workup, improved yields, and the use of water as the solvent that is considered to be relatively environmentally benign.

A facile, efficient, and environmentally friendly procedure for the synthesis of 2,3-dihydroquinazolin-4(1H)-ones from isatoic anhydride, aldehyde, and ammonium acetate in the presence of thiamine hydrochloride (VB1) in EtOH is described. The protocol proves to be efficient and environmentally benign in terms of high yields, ease of recovery, and reusability of catalyst.

A facile method of synthesizing 8-oxoprotoberberines is described from 6-benzoyl-5,6,7,8-tetrahydro-[1,3]dioxolo[4,5-g]isoquinoline-5-carbaldehyde via acid-mediated cyclization or from 2-(2-iodophenethyl)isoquinolin-1(2H)-one via the Heck reaction. The present method offers several advantages, such as good yields and a simple procedure.

A new, one-pot, four-component condensation of 3-methyl-1H-pyrazol-5(4H)-one, ammonium acetate, aromatic aldehydes, and meldrum’s acid in [bmim]BF4 as solvent is described for the synthesis of 3-(5-amino-3-methyl-1H-pyrazol-4-yl)-3-arylpropanoic acid derivatives. This methodology resulting in excellent isolated yields in short reaction time is characterized by simple work up procedure and little environmental impact.

A facile and efficient protocol is described for the synthesis of 4-aryl-1,4,7,8-tetrahydro-3,5-dimethyldipyrazolo[3,4-b:4′,3′-e]pyridine derivatives in good yields by the condensation of 3-methyl-1H-pyrazol-5(4H)-one, aromatic aldehydes, and ammonium acetate under catalyst-free conditions. The advantages of this protocol are operational simplicity, mild reaction conditions, high yields, and little environmental impact.