Synthesis of Diketohexenoic Acid Derivatives by Alkenylation of Indoles and Pyrroles with 4-Pyrones

2,6-Dicyano-4-pyrone as a Novel and Multifarious Building Block for the Synthesis of 2,6-Bis(hetaryl)-4-pyrones and 2,6-Bis(hetaryl)-4-pyridinols

In this work, a three-stage and easily scalable synthesis of 2,6-dicyano-4-pyrone (overall yield of 45%) as a new convenient building block has been developed from diethyl acetonedioxalate. It was shown that the transformation with hydroxylamine and [3 + 2]-cycloaddition, in contrast to the reactions with hydrazines, selectively proceed through the attack at the cyano groups without the pyrone ring-opening to give symmetrical and unsymmetrical pyrone-bearing heterocyclic triads containing 1,2,4- and 1,3,4-oxadiazoles as well as tetrazole moieties. The reaction of 2,6-bis(hetaryl)-4-pyrones with ammonia afforded 2,6-bis(hetaryl)pyridines in 63-87% yields. The 4-pyridone/4-pyridinol tautomerism of 2,6-bis(hetaryl)pyridinols and the influence of the nature of adjacent azolyl moieties on this equilibrium have been discussed.

Synthesis of novel polycarbonyl Schiff bases by ring-opening reaction of ethyl 5-acyl-4-pyrone-2-carboxylates with primary mono- and diamines

An approach for the introduction of the tricarbonyl moiety into aromatic, heterocyclic, and aliphatic amines with the use of acylpyrones has been developed for the synthesis and the design of novel polycarbonyl Schiff base ligands, including salphen structures. This Michael addition–ring-opening reaction proceeds under mild conditions (stirring at 0–20 °C) via the attack at the C-6 position of the pyrone ring in good to high yields (up to 99%) with excellent selectivity. The products can be easily isolated by crystallization without the use of chromatography. The scope of the reaction, tautomeric equilibrium of open-chain products, and their cyclization into pyridone structures were investigated.

An approach for the introduction of the tricarbonyl moiety into various amines has been developed based on acylpyrones.

A chemo- and regiocontrolled approach to bipyrazoles and pyridones via the reaction of ethyl 5-acyl-4-pyrone-2-carboxylates with hydrazines

Chemo- and regiocontrolled syntheses of pyrazoles and pyridones are presented on the basis of 4-pyrones. A novel approach towards highly functionalized 3,4'-bipyrazoles has been developed by using reactions of ethyl 5-acylcomanoates with hydrazines. The acid-promoted double cyclocondensation allows switching of the structure of the pyrazole rings easily through changing both the nature of hydrazine and the reaction conditions. The transformation of 4-pyrones with phenylhydrazine in EtOH at -20 °C leads to hydroxypyridones as monoaddition products which can be used as precursors for the preparation of pyridone and pyrazole derivatives. A novel rearrangement of 2-hydroxypyridone to pyrazolyl-1,3-diketones in DMSO was found. The structure and regiochemistry of bipyrazoles were confirmed by X-ray analysis and 2D NMR experiments.