Sequential four-component protocol for the synthesis of pyrido[1,2-a]pyrimidin-6-one derivatives in water

p-Toluenesulfonic acid-promoted organic transformations for the generation of molecular complexity

“…105 A very efficient and environmentally friendly synthesis of functionalized 9-nitro-1,2,3,4,7,8-hexahydro-6 H -pyrido[1,2- a ]pyrimidin-6-ones is obtained by Rezvanian et al in aqueous medium (Scheme 64). 106 This synthesis substantially contributes to achieving the requirements of green chemistry because it is a simple, one-pot four-component transformation of benzaldehydes, 1,1-bis(methylthio)-2-nitroethylene, Meldrum's acid, and various diamines using water as the reaction medium and is catalysed by p -TSA. Initial Knoevenagel condensation between aromatic aldehyde and Meldrum's acid generated the intermediate A42 .…”

The Molecular Diversity Scope of Meldrum's Acid in Multicomponent Reactions

“…[58] A greener high-yielding reaction of Meldrum's acid 1, benzaldehydes 13, 1,1-bis(methythio)-2-nitroethylene 119, and diamines 60 catalyzed by a p-toluene sulfonic acid (PTSA) in H 2 O under reflux ambient was designed by Rezvanian and co-workers to produce 9-nitro-1,2,3,4,7,8hexahydro-6H-pyrido[1,2-a]pyrimidin-6-ones 120 (Scheme 53). [59] addition of -NH to Meldrum's carbonyl group, the elimination of an acetone molecule and then the loss of a CO 2 molecule, to offer the target molecule 120.…”

“…A greener high‐yielding reaction of Meldrum's acid 1 , benzaldehydes 13 , 1,1‐bis(methythio)‐2‐nitroethylene 119 , and diamines 60 catalyzed by a p ‐toluene sulfonic acid (PTSA) in H 2 O under reflux ambient was designed by Rezvanian and co‐workers to produce 9‐nitro‐1,2,3,4,7,8‐hexahydro‐6H‐pyrido[1,2‐ a ]pyrimidin‐6‐ones 120 (Scheme 53). [59] …”

A New Efficient One‐Pot Three‐Component Synthesis of Diverse Pyrido[1,2‐a]pyrimidines

“…Thus, tetrahydropyrido[1,2-a]pyrimidines were obtained by one-pot protocols based on cyclizations of 1,1bis(methylthio)-2-nitroethylene, propanediamine, malononitrile with isatines (or arylaldehydes) without solvent under nano-Fe 3 O 4 -GO-SO 3 H catalysis [17] or with substituted salicylaldehyde in refluxing ethanol [18] as well as by domino reactions of dihydropyrimidin-2-tione and alkynes with α,β-unsaturated carboxylic acids in the presence of Cu 2 O. [19] For the synthesis of hexahydropyrido[1,2-a]pyrimidin-6-ones, a four-and five-component approaches based on cyclizations of 1,1-bis(methylthio)-2-nitroethylene, aldehydes, propanediamine with Meldrum acid in water [20] or with primary amines and diketene in ethanol [21] have been developed.…”