N,N,N′,N′‐Tetramethylchloroformamidinium Chloride‐Mediated Cyclizations of β‐Oxo Amides: Facile and Divergent One‐Pot Synthesis of Substituted 2H‐Pyrans, 4H‐Pyrans and Pyridin‐2(1H)‐ones

Abstract

An efficient and divergent one-pot synthesis of substituted 2H-pyrans, 4H-pyrans and pyridin-2(1H)-ones from b-oxo amides based on the selection of the reaction conditions is reported. Mediated by N,N,N',N'-tetramethylchloroformamidinium chloride, b-oxo amides underwent intermolecular cyclizations in the presence of triethylamine at room temperature to give substituted 2H-pyrans in high yields, which could be converted into substituted 4H-pyrans in the presence of sodium hydroxide in ethanol at room temperature, or into substituted pyridin-2-

[5C + 1N] Annulations: Two Novel Routes to Substituted Dihydrofuro[3,2-c]pyridines

“…On the basis of the above experimental results together with some literature reported, a plausible mechanism for the synthesis of 2,3-dihydrofuro[3,2- c ]pyridines 2 from cyclopropanes 1 is proposed as depicted in Scheme . The attack of ammonia on the carbon–carbon double bond of 1 at high temperature triggers the transformation and induces a regioselective ring-enlargement to generate intermediate A , , followed by an intramolecular aza-nucleophilic addition and elimination to form bicyclic intermediate B , which then undergoes dehydration reaction to give rise to the final product 2,3-dihydrofuro[3,2- c ]pyridine of type 2 . It should be noted that the added cyclopropane ring of 1 makes it possible to construct pyridine skeleton in the presence of amonia in this work, which is different from the traditional formal [5C + 1N] annulation of 1,5-dicarbonyl compounds and their equivalents with ammonia, Guareschi–Thorpe condensation, or Hantzsch reaction …”

POCl3‐Mediated Reaction: A New Entry to Polysubstituted 2‐Pyridones via Self‐condensation of β‐Keto Amides

“…β‐Keto amide or their derivatives are important precursors of bioactive and functional materials, especially in the construction of heterocyclic systems because of its specific six reactive sites in the same molecule . Considering the environmental concerns, yield, and safety, thus, the development of a new method for the direct synthesis of 2‐pyrones is highly critical.…”

Efficient and divergent synthesis of polyfunctionalized 2-pyridones from β-keto amides

“…b-Keto amide and their derivatives have been proven to be the important starting materials and reagents in the construction of heterocyclic systems since they possess six reactive sites in the same molecule. [28][29][30][31][32][33][34][35] They have also been used as building blocks for the construction of biologically interesting heterocycles. 36 So far, a number of natural product-like heterocyclic compounds have been successfully synthesized based on b-keto amide and their derivatives.…”