Trimesic acid-functionalized chitosan: A novel and efficient multifunctional organocatalyst for green synthesis of polyhydroquinolines and acridinediones under mild conditions

Trimesic acid-functionalized chitosan (Cs/ECH-TMA) material was prepared through a simple procedure by using inexpensive and commercially available chitosan (Cs), epichlorohydrin (ECH) linker and trimesic acid (TMA). The obtained bio-based Cs/ECH-TMA material was characterized using energy-dispersive X-ray (EDX) and Fourier-transform infrared (FTIR) spectroscopy, field emission scanning electron microscopy (FESEM) and X-ray diffraction (XRD) analysis. The Cs/ECH-TMA material was successfully used, as a multifunctional heterogeneous and sustainable catalyst, for efficient and expeditious synthesis of medicinally important polyhydroquinoline (PHQ) and polyhydroacridinedione (PHA) scaffolds through the Hantzsch condensation in a one-pot reaction. Indeed, the heterogeneous Cs/ECH-TMA material can be considered as a synergistic multifunctional organocatalyst due to the presence of a large number of acidic active sites in its structure as well as hydrophilicity. Both PHQs and PHAs were synthesized in the presence of biodegradable heterogeneous Cs/ECH-TMA catalytic system from their corresponding substrates in EtOH under reflux conditions and high to quantitative yields. The Cs/ECH-TMA catalyst is recyclable and can be reused at least four times without significant loss of its catalytic activity.

In Melting Points We Trust: A Review on the Misguiding Characterization of Multicomponent Reactions Adducts and Intermediates

We discuss herein the problems associated with using melting points to characterize multicomponent reactions’ (MCRs) products and intermediates. Although surprising, it is not rare to find articles in which these MCRs final adducts (or their intermediates) are characterized solely by comparing melting points with those available from other reports. A brief survey among specialized articles highlights serious and obvious problems with this practice since, for instance, cases are found in which as many as 25 quite contrasting melting points have been attributed to the very same MCR adduct. Indeed, it seems logical to assume that the inherent non-confirmatory nature of melting points could be vastly misleading as a protocol for structural confirmation, but still many publications (also in the Q1 and Q2 quartiles) insist on using it. This procedure contradicts best practices in organic synthesis, and articles fraught with limitations and misleading conclusions have been published in the MCRs field. The drawbacks inherent to this practice are indeed serious and have misguided MCRs advances. We therefore suggest some precautions aimed at avoiding future confusions.

Ammonium metavanadate (NH4VO3): a highly efficient and eco-friendly catalyst for one-pot synthesis of pyridines and 1,4-dihydropyridines

In this study, we reported the ammonium metavanadate (NH₄VO₃) as an efficient, cost-effective, and mild catalyst for the synthesis of substituted pyridines via a one-pot pseudo four-component reaction. Furthermore, we investigated Hantzsch 1,4-dihydropyridines (1,4-DHPs) synthesis and oxidation of 1,4-DHPs to their corresponding pyridines. The present approach offers a rapid methodology for accessing various pyridines with broad functional group tolerance and good yields using NH₄VO₃ catalyst as a green catalyst.

Multicomponent diversity-oriented synthesis of symmetrical and unsymmetrical 1,4-dihydropyridines in recyclable glycine nitrate (GlyNO3) ionic liquid: a mechanistic insight using Q-TOF, ESI-MS/MS

Glycine nitrate (GlyNO₃) ionic liquid has been explored for the synthesis of symmetrical and unsymmetrical 1,4-DHPs in good-to-excellent yields with mechanistic studies using Q-TOF and ESI-MS/MS.

Diethyl 4-(2,4-dichloro-phen-yl)-2,6-dimethyl-1,4-dihydro-pyridine-3,5-dicarboxyl-ate

In the title compound, C₁₉H₂₁Cl₂NO₄, the dihydro­pyridine ring adopts a flattened boat conformation. The dichloro­phenyl ring is oriented almost perpendicular to the planar part of the dihydro­pyridine ring [dihedral angle = 89.1 (1)°]. An intra­molecular C—H⋯O hydrogen bond is observed. In the crystal structure, mol­ecules are linked into chains along the b axis by N—H⋯O hydrogen bonds

Microwave Heating in Conjunction with UV Irradiation: a Tool for the Oxidation of 1,4-Dihydropyridines to Pyridines

Microwave heating is used for the preparation of 1,4-dihydropyridines and then, in conjunction with UV irradiation, is used for the efficient oxidation of the 1,4-dihydropyridines to pyridines. The oxidation reactions are performed in a sealed vessel using oxygen as the oxidant and an electrodeless discharge lamp as the irradiation source.

Three-Component One-Pot Synthesis of Unsymmetrical 1,4-dihydropyridine Derivatives in Aqueous Media

A series of methyl ethyl 2,6-dimethyl-4-substituted-1,4-dihydropyridine-3,5-dicarboxylates were synthesised by the three-component reaction of aldehydes, ethyl acetoacetate and methyl β-aminocrotonate in the presence of triethylbenzylammonium chloride (TEBAC) in aqueous medium. This method has the advantage of good yields.

Magnesium nitride as a convenient source of ammonia: preparation of dihydropyridines

Magnesium nitride (Mg 3N 2) has been investigated for the preparation of dihydropyridines. This is a commercially available, bench-stable solid that generates ammonia upon treatment with protic solvents. The main features of the process are the facile reaction setup and good yields obtained in the majority of cases.

Sulfated zirconia-catalyzed synthesis of 3,4-dihydropyrimidin-2(1H)-ones (DHPMs) under solventless conditions: competitive multicomponent Biginelli vs. Hantzsch reactions

The catalytic ability of ZrO(2)/SO(4)(2-) to promote solventless three-component condensation reactions of a diversity of aromatic aldehydes, urea or thoiurea and ethyl acetoacetate was studied. Products resulting from Hantzsch and/or Biginelli multi-component reactions are obtained in the presence of solid acid catalysts using the same reactants but different temperature conditions. The sulfated zirconia catalyst can be recovered and recycled in subsequent reactions with a gradual decrease of activity.