Metal‐Free Assemblage of Four C−N and Two C−C Bonds via a Cascade Five Component Diastereoselective Synthesis of Pyrido[1,2‐a]Pyrimidines

Abstract

An efficient heteroannulation synthesis of N‐fused, pyrido[1,2‐a]pyrimidines was successfully achieved via a sequential, one‐pot five‐component reaction, involving primary amines, diketene (DK), differently substituted aromatic aldehydes, nitro ketene dithioacetal and propanediamine in ethanol at 70 °C. This new protocol constructs two rings through the formation of four C–N and two C–C bonds via a one pot sequential reaction involving ring‐opening/ Knoevenagel condensation, /nucleophilic substitution (SN)/ Michael addition followed by imine−enamine tautomerization and final N‐heterocyclization. The method is particularly attractive due to the advantages such as: atom economy, optimum convergence, commercially available or readily accessible starting materials, high bond‐forming efficiency, free metal‐catalyst and mild reaction conditions. The products were isolated by just decantation of the solvent and purification without using column chromatography method.

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.…”

Chemo‐ and diastereoselective synthesis of new oxa[3.3.3]propellane via a domino cascade four‐component reaction based on diketene

“…In continuation of our interest in the development of newsynthetic procedures in heterocyclic chemistry, [ 25 ] particularly those which are provided through multicomponent reaction [ 24,26 ] and especially using diketene as one of the vital component [ 27 ] herein, we wish to describe a one‐pot, multi‐component, metal‐free, chemo and diastereoselective synthesis of oxa[3.3.3]propellane derivatives via one‐pot four‐component reaction in the presence of Et 3 N at room temperature in EtOH.…”