Multicomponent Synthesis of 2-(2,4-Diamino-3-cyano-5H-chromeno[2,3-b]pyridin-5-yl)malonic Acids in DMSO

Thermal Rearrangement of 5-(2-Hydroxy-6-oxocyclohexyl)-5H-chromeno[2,3-b]pyridines

Some of the most important transformations in organic chemistry are rearrangement reactions, which play a crucial role in increasing synthetic efficiency and molecular complexity. The development of synthetic strategies involving rearrangement reactions, which can accomplish synthetic goals in a very efficient manner, has been an evergreen topic in the synthetic chemistry community. Xanthenes, pyridin-2(1H)-ones, and 1,6-naphthyridines have a wide range of biological activities. In this work, we propose the thermal rearrangement of 7,9-dihalogen-substituted 5-(2-hydroxy-6-oxocyclohexyl)-5H-chromeno[2,3-b]pyridines in DMSO. Previously unknown 5,7-dihalogenated 5-(2,3,4,9-tetrahydro-1H-xanthen-9-yl)-6-oxo-1,6-dihydropyridines and 10-(3,5-dihalogen-2-hydroxyphenyl)-5,6,7,8,9,10-hexahydrobenzo[b][1,6]naphthyridines were synthesized with excellent yields (90–99%). The investigation of the transformation using 1H-NMR monitoring made it possible to confirm the ANRORC mechanism. The structures of synthesized compounds were confirmed by 2D-NMR spectroscopy.

2,4-Diamino-5-(5-hydroxy-1-phenyl-3-(trifluoromethyl)-1H-pyrazol-4-yl)-5H-chromeno[2,3-b]pyridine-3-carbonitrile

5H-Chromeno[2,3-b]pyridines are important compounds with industrial, biological, and medicinal properties. In this short note, the multicomponent reaction of salicylaldehyde, malononitrile dimer, and 2-phenyl-5-(trifluoromethyl)-2,4-dihydro-3H-pyrazol-3-one in dimethyl sulfoxide at ambient temperature was investigated to give 2,4-diamino-5-(5-hydroxy-1-phenyl-3-(trifluoromethyl)-1H-pyrazol-4-yl)-5H-chromeno[2,3-b]pyridine-3-carbonitrile with good yield. The structure of the previously unknown chromeno[2,3-b]pyridine derivative was confirmed by elemental analysis, mass, nuclear magnetic resonance, and infrared spectroscopy data. The ADME (absorption, distribution, metabolism, and excretion) properties were also assessed.

One-Pot Solvent-Involved Synthesis of 5-O-Substituted 5H-Chromeno[2,3-b]pyridines

Chromeno[2,3-b]pyridines are substances demanded in medicinal and material chemistry. PASE (pot, atom, and step economy) and in particular one-pot approaches are key green chemistry techniques that are applied for the synthesis of heterocyclic compounds. In this case, the PASE approach was extended with 'component economy', as solvent was used also as reactant (solvent-involved reaction). This approach was adopted for the one-pot synthesis of previously unknown O-substituted 5-alkoxy-5H-chromeno[2,3-b]pyridines via two-step transformation, namely the reaction of salicylaldehydes and malononitrile dimer, with the subsequent addition of alcohol. The mechanistic studies revealed the possibility of concurrent reaction. The studies aided in optimizing the reaction conditions for the best yields (77-93%). Thus, the one-pot reaction proceeds efficient and quickly, and the work-up procedure (only simple filtering) is very convenient. The structure of synthesized chromeno[2,3-b]pyridines was confirmed by 2D NMR spectroscopy.

2,4-Diamino-5-(5-amino-3-oxo-2,3-dihydro-1H-pyrazol-4-yl)-5H-chromeno[2,3-b]pyridine-3-carbonitrile

The one-pot synthesis methodology has become the leading atom-economical approach for various chemical transformations in a single pot, without purifying intermediate compounds. Chromeno[2,3-b]pyridines are an important class of heterocyclic compounds with versatile biological profiles and other different applications The 5-aminopyrazole system represents a significant heterocyclic template that has gained considerable interest because of its long history of use in the pharmaceutical and agrochemical industries. In this communication, the one-pot transformation of salicylaldehyde, malononitrile dimer, and 2-cyanoacetohydrazide in an ethanol/pyridine mixture was investigated to provide 2,4-diamino-5-(5-amino-3-oxo-2,3-dihydro-1H-pyrazol-4-yl)-5H-chromeno[2,3-b]pyridine-3-carbonitrile in good yield. The structure of the novel compound was confirmed by means of elemental analysis, mass-, nuclear magnetic resonance, and infrared spectroscopy.

Efficient regioselective five-component synthesis of novel thiazolo[3,2-a]pyridine carbohydrazides and oxazolo[3,2-a]pyridine carbohydrazides

Two new categories of fused pyridines include 2H-thiazolo[3,2-a]pyridine-6-carbohydrazides and 2H-oxazolo[3,2-a]pyridine-6-carbohydrazides have been successfully synthesized via five-component cascade reactions using 9-fluorenone, cyanoacetohydrazide, 1,1-bis(methylthio)-2-nitroethene, aromatic aldehydes and cysteamine hydrochloride or ethanol amine as starting materials. This new approach involves a subsequence of key steps: N,S-acetal or N,O-acetal formation, Knoevenagel condensation, Michael addition, tautomerization and N-cyclization. It also has some advantages, such as convenience of operation, tolerance of a wide diversity of functional groups, use of green solvent and ease of purification by washing the crude products with ethanol.

2,4-Diamino-5-(nitromethyl)-5H-chromeno[2,3-b]pyridine-3-carbonitrile

Dimethyl sulfoxide (DMSO) is a cheap polar aprotic solvent used in organic synthesis and in pharmacology because of its low cost, high stability, and non-toxicity. Multicomponent reactions (MCRs) are highly convergent processes and have good atom, step, and pot economies. In this communication, the multicomponent transformation of salicylaldehyde, malononitrile dimer, and nitromethane in DMSO at room temperature was investigated to give 2,4-diamino-5-(nitromethyl)-5H-chromeno[2,3-b]pyridine-3-carbonitrile in good yield. The structure of the earlier unknown compound was confirmed by means of elemental analysis, mass-, nuclear magnetic resonance, and infrared spectroscopy.

Dimethyl 2-(2,4-Diamino-3-cyano-5H-chromeno[2,3-b]pyridin-5-yl)malonate

Dimethyl sulfoxide (DMSO) is widely used as a solvent in organic synthesis and in pharmacology because of its low cost, stability, and non-toxicity. Multicomponent reactions are a powerful synthetic tool for the rapid and efficient construction of complicated molecular frameworks. In this communication, the multicomponent transformation of salicylaldehyde, malononitrile dimer, and dimethyl malonate in DMSO at room temperature was carefully investigated to give dimethyl 2-(2,4-diamino-3-cyano-5H-chromeno[2,3-b]pyridin-5-yl)malonate with good yield. The structure of the new compound was established by means of elemental analysis and mass, nuclear magnetic resonance, and infrared spectroscopy.