A Straightforward Approach for the Stereoselective Synthesis of (E)-2-Aryl/vinylmethylidene-1,4-benzodiazepines and -1,4-benzodiazepin-5-ones through Palladium/Charcoal-Catalyzed Reactions

Synthetic aspects of 1,4- and 1,5-benzodiazepines using o-phenylenediamine: a study of past quinquennial

Benzodiazepines, seven-membered heterocyclic compounds having two nitrogen atoms at different positions, are ruling scaffolds in the area of pharmaceutical industry. They act as cardinal moieties in organic synthesis as well as in medicinal chemistry. Among the different benzodiazepines, 1,4- and 1,5-benzodiazepines play a far-reaching role in the field of biological activities such as anticonvulsion, anti-anxiety, sedation, and hypnotics. In the past few decades, researchers have conducted a lot of work on these moieties and developed broad, valuable, and significant approaches for their synthesis. In this review article, we recapitulate the systematic synthetic strategies of 1,4- and 1,5-benzodiazepines using o-phenylenediamine as a precursor over the past five years (2018-2022). This article will be helpful for scientists and researchers to examine and explore novel and efficient methods for the synthesis of these biologically active moieties.

Enantioenriched α-Vinyl 1,4-Benzodiazepines and 1,4-Benzoxazepines via Enantioselective Rhodium-Catalyzed Hydrofunctionalizations of Alkynes and Allenes

Benzofused seven-membered heterocycles such as 1,4-benzo[e]diazepines (1,4-BZDs) and 1,4-benzo[e]oxazepines (1,4-BZOs) were efficiently synthesized by Rh-catalyzed hydrofunctionalization of internal alkynes and allenes in good to excellent yields. The asymmetric hydroamination of (aminomethyl)anilines gave rise to 3-vinyl-1,4-BZDs with excellent enantioselectivities. Orthogonal N-deprotection of 1,4-BZDs allowed an easy entry to an advanced pyrrolobenzodiazepine metabolite of the V₂-receptor antagonist Lixivaptan.

Efficient Construction of 5H-1,4-Benzodiazepine Derivatives by a Catalyst-Free Direct Aerobic Oxidative Annulation Strategy

A catalyst-free direct aerobic oxidative annulation reaction of 2-aminobenzylic amines and α-hydroxy ketones efficiently afforded versatile 5H-1,4-benzodiazepine derivatives by employing air as economic and green oxidant under mild conditions. Interestingly, solvent was found to be crucial to the reaction, so that by using acetic acid as the best solvent an efficient and practical method could be achieved, requiring no catalysts or additives at all. This method tolerates a wide range of 2-aminobenzylic amines and α-hydroxy ketones and could be scaled up to multigram synthesis and directly applied in one-step synthesis of the pharmaceutically active N-desmethylmedazepam derivatives, revealing the potential of this new method in the synthesis of 5H-1,4-benzodiazepine skeleton-based pharmaceuticals and chemicals.

Synthesis of Highly Conjugated Functionalized 2-Pyridones by Palladium-Catalyzed Aerobic Oxidative Dicarbonation Reactions of N-(Furan-2-ylmethyl) Alkyne Amides and Alkenes as Coupling Partners

A mild, step-economical method for the synthesis of highly conjugated functionalized 2-pyridones from N-(furan-2-ylmethyl) alkyne amides is reported. This method involves Pd-catalyzed aerobic oxidative dicarbonation reactions of alkynes with carbon nucleophiles of a furan ring and an acrylate or styrene as coupling partners. The UV-vis absorption spectra of some of the 2-pyridones indicated that they absorbed shortwave radiation, suggesting their potential utility for filtration of such radiation.

Metal-free synthesis of 1,4-benzodiazepines and quinazolinones from hexafluoroisopropyl 2-aminobenzoates at room temperature

Herein, we describe the novel reactivity of hexafluoroisopropyl 2-aminobenzoates. The metal-free synthesis of 1,4-benzodiazepines and quinazolinones from hexafluoroisopropyl 2-aminobenzoates has been developed at room temperature. These procedures feature good functional group tolerance, mild reaction conditions, and excellent yields. The newly formed products can readily be converted to other useful N-heterocycles. Moreover, the products and their derivatives showed potent anticancer activities in vitro by MTT assay.

A metal-free synthesis of 1,4-benzodiazepines and quinazolinones from hexafluoroisopropyl 2-aminobenzoates has been developed at room temperature.

Palladium-Catalyzed Benzodiazepines Synthesis

This review is focused on palladium-catalyzed reactions as efficient strategies aimed at the synthesis of different classes of benzodiazepines. Several reaction typologies are reported including hydroamination, amination, C–H arylation, N-arylation, and the Buchwald–Hartwig reaction, depending on the different substrates identified as halogenated starting materials (activated substrates) or unactivated unsaturated systems, which then exploit Pd(0)- or Pd(II)-catalytic species. In particular, the use of the domino reactions, as intra- or intermolecular processes, are reported as an efficient and eco-compatible tool to obtain differently functionalized benzodiazepines. Different domino reaction typologies are the carboamination, aminoarylation, aminoacethoxylation, aminohalogenation, and aminoazidation.

Synthesis of Benzodiazepines Through Ring Opening/Ring Closure of Benzimidazole Salts

Pyrido-benzodiazepine derivatives are undoubtedly one of the most important structural motifs in the marketed drugs and the drug candidates. Commonly synthetic methods for construction of the benzodiazepine ring derivatives are based on the condensation reactions of two highly functionalized synthons. The development of synthesis for these compounds, however, is hampered by the regioselectivity and atom economy. In this work, a one-step synthesis of pyrido-benzodiazepine backbones and its analogues is achieved through continuous ring-opening hydrolysis of benzimidazole salts and intramolecular C-H bond activation. The reaction mechanism is explored by control experiments and density functional theory (DFT) calculations.

Palladium-Catalyzed Regioselective Syn-Chloropalladation-Olefin Insertion-Oxidative Chlorination Cascade: Synthesis of Dichlorinated Tetrahydroquinolines

A palladium catalyzed cascade process involving syn-chloropalladation, intramolecular olefin insertion, and oxidative C-Cl bond formation reactions was demonstrated for the synthesis of dichlorinated tetrahydroquinolines in high yields (up to 93%). The N-propargyl arylamines having a tethered α,β-unsaturated carbonyl moiety underwent a regioselective syn-chloropalladation followed by a Heck-type reaction to deliver the tetrahydroquinoline scaffold. The rare insertion of the second chlorine atom was rationalized comprising a Pd^II/IV catalytic cycle and oxidative cleavage of the C-Pd^II bond.

Palladium-catalysed stereoselective synthesis of 4-(diarylmethylidene)-3,4-dihydroisoquinolin-1(2H)-ones: expedient access to 4-substituted isoquinolin-1(2H)-ones and isoquinolines

Palladium-catalysed stereoselective synthesis of 4-(diarylmethylidene)-3,4-dihydroisoquinolin-1(2H)-ones and their straightforward transformations to 4-substituted isoquinolin-1(2H)-ones and isoquinolines are described.