Azetidin-2-one, a four-membered cyclic lactam (beta-lactam) skeleton has been recognised as a useful building block for the synthesis of a large number of organic molecules by exploiting the strain energy associated with it, in addition to its use in the synthesis of a variety of beta-lactam antibiotics. Efforts have been made in exploring such new aspects of beta-lactam chemistry using enantiomerically pure beta-lactams as versatile intermediates for the synthesis of aromatic beta-amino acids and their derivatives, peptides, polyamines, polyamino alcohols, amino sugars and polyamino ethers. The development of methodologies based on beta-lactam nucleus is now referred as 'the beta-lactam synthon methods'. The selective bond cleavage of the strained ring coupled with further interesting transformation render this fascinating molecule as a powerful building block. This provides an access to diverse structural type of synthetic target molecules lacking beta-lactam ring structure. This review provides an account of synthesis of organic compounds having biological significance at the same time lacking beta-lactam ring, by using beta-lactam as synthon.

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An efficient synthesis of pyrazolopyranopyrimidines was achieved by four component domino reaction of aldehydes, barbituric acid, hydrazine hydrate, and ethyl acetoacetate using biodegradable and recyclable choline chloride:urea as deep eutectic solvent. The reaction proceeds rapidly and affords the corresponding diverse tricyclic fused pyrazolopyranopyrimidines with a good to excellent yield. The protocol has the advantage of easy workup, high yields, and an environmentally benign methodology compared with other reported methods. The simplicity of this method makes it an interesting alternative to other approaches.

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