New protocols for the synthesis of 3,4-annulated and 4-substituted quinolines from β-bromo-α,β-unsaturated aldehydes and 1-bromo-2-nitrobenzene or 2-bromoacetanilide

Synthesis and biological activities of bicyclic pyridines integrated steroid hybrid

Reports on structural modification of heterosteroids through various reactions, and developed synthetic routes have considerably increased over the last decade. The present review encompasses the applicable approaches dealing with the utility of reactive moieties in various steroids for the synthesis of fused bicyclic pyridines, and binary bicyclic pyridines all over the years. The different sections include the synthesis of steroids-fused, and binary quinolines, pyridopyrimidines, imidazopyridines, spirocyclic imidazopyridines, pyrazolopyridines, thienopyridines, pyridinyl-thiazoles, and tetrazolopyridine hybrids, as well as, the diverse biological applications of these heterocyclic steroids. The researchers' interest was principally focused on investigating the flexibility of synthetic strategies for various derivatives of natural steroids and building proposals based on heterocyclic steroids for drug discovery, biological assessments, and synthetic applications.

Synthesis of indenophenanthridine via a [4+2] annulation strategy: a “turn-off’’ Fe3+ ion sensor, practical application in live cell imaging and reversible acidochromism studies

An efficient protocol has been developed for the synthesis of a novel fluorescent probe, 1,2-disubstituted-indeno[1,2,3-gh]phenanthridine, derived from a series of α-oxo-ketene dithioacetals (OKDTAs) and indenoquinoline under essential conditions via a [4+2] annulation in excellent yield.

Nickel catalyzed synthesis of 4,4′-bichromenes/4,4′-bithiochromenes and their Atropisomerism

4,4′-bichromenes and 4,4′-bithiochromenes have been synthesized by a Ni catalyzed homocoupling method and their Atropisomeric behavior has been studied.

The Palladium-Catalyzed Ullmann Cross-Coupling Reaction: A Modern Variant on a Time-Honored Process

Cross-coupling reactions, especially those that are catalyzed by palladium, have revolutionized the way in which carbon-carbon bonds can be formed. The most commonly deployed variants of such processes are the Suzuki-Miyaura, Mizoroki-Heck, Stille, and Negishi cross-coupling reactions, and these normally involve the linking of an organohalide or pseudohalide (such as a triflate or nonaflate) with an organo-metallic or -metalloid such as an organo-boron, -magnesium, -tin, or -zinc species. Since the latter type of coupling partner is often prepared from the corresponding halide, methods that allow for the direct cross-coupling of two distinct halogen-containing compounds would provide valuable and more atom-economical capacities for the formation of carbon-carbon bonds. While the venerable Ullmann reaction can in principle achieve this, it has a number of drawbacks, the most significant of which is that homocoupling of the reaction partners is a competitive, if not the dominant, process. Furthermore, such reactions normally occur only under forcing conditions (viz., often at temperatures in excess of 250 °C). As such, the Ullmann reaction has seen only limited application in this regard, especially as a mid- to late-stage feature of complex natural product synthesis. This Account details the development of the palladium-catalyzed Ullmann cross-coupling reaction as a useful method for the assembly of a range of heterocyclic systems relevant to medicinal and/or natural products chemistry. These couplings normally proceed under relatively mild conditions (<100 °C) over short periods of time and, usually, to the exclusion of (unwanted) homocoupling events. The keys to success are the appropriate choice of coupling partners, the form of the copper metal employed, and the choice of reaction solvent. At the present time, the cross-coupling partners capable of engaging in the title reaction are confined to halogenated and otherwise electron-deficient arenes and, as complementary reactants, α- or β-halogenated, α,β-unsaturated aldehydes, ketones, esters, lactones, lactams, and cycloimides. Nitro-substituted (and halogenated) arenes, in particular, serve as effective participants in these reactions, and the products of their coupling with the above-mentioned carbonyl-containing systems can be manipulated in a number of different ways. Depending on the positional relationship between the nitro and carbonyl groups in the cross-coupling product, the reduction of the former group, which can be achieved under a range of different conditions, provides, through intramolecular nucleophilic addition reactions, including Schiff base condensations, access to a diverse range of heterocyclic systems. These include indoles, quinolines, quinolones, isoquinolines, carbazoles, and carbolines. Tandem variants of such cyclization processes, in which Raney cobalt is used as a catalyst for the chemoselective reduction (by dihydrogen) of nitro and nitrile groups (but not olefins), allow for the assembly of a range of structurally challenging natural products, including marinoquinoline A, (±)-1-acetylaspidoalbidine, and (±)-gilbertine.

Palladium-Catalyzed Ullmann Cross-Coupling of β-Iodoenones and β-Iodoacrylates with o-Halonitroarenes or o-Iodobenzonitriles and Reductive Cyclization of the Resulting Products To Give Diverse Heterocyclic Systems

The palladium-catalyzed Ullmann cross-coupling of β-iodoenones and β-iodoacrylates such as 5 (X = I) with o-halonitroarenes and o-iodobenzonitriles including 2 affords products such as compound 7. These can be engaged in a range of reductive cyclization reactions leading to heterocyclic frameworks such as 3,4-benzomorphan derivative 43.

Hydride-induced anionic cyclization: an efficient method for the synthesis of 6-H-phenanthridines via a transition-metal-free process

A novel procedure for hydride-induced anionic cyclization has been developed. It includes the reduction of a biaryl bromo-nitrile with a nucleophilic aromatic substitution (S(N)Ar). A range of polysubstituted 6-H-phenanthridines were so obtained in moderate to good yield with good substrate tolerance. This method involves a concise transition-metal-free process and was applied to synthesize natural alkaloids.

Tandem catalytic oxidative deacetylation of acetoacetic esters and heteroaromatic cyclizations

Coupling of ethyl acetoacetate with MVK and with 2-nitrobenzyl bromides, Mn(iii)/Co(ii)-catalyzed deacetylation, and heterocyclizations provide pyrroles and indoles, respectively.

Palladium-catalyzed Suzuki-Miyaura coupling of aryl sulfamates with arylboronic acids

Readily available NHC-Pd(II)-Mp complexes 2 showed efficient catalytic activity toward the Suzuki-Miyaura coupling of aryl sulfamates with arylboronic acids or potassium phenyltrifluoroborate, giving the expected coupling products in good to high yields. It should be noted that this is the first example so far of the phosphine-free, NHC-Pd(II) complexes catalyzed Suzuki-Miyaura coupling of aryl sulfamates with arylboronic acids.

A microwave promoted solvent-free approach to steroidal quinolines and their in vitro evaluation for antimicrobial activities

The preparation of A-ring and D-ring fused steroidal quinolines is described from one-pot reaction of steroidal β-bromovinylaldehydes and arylamines in solvent-free and catalyst-free condition under microwave irradiation. The antimicrobial activities of the compounds were tested by agar diffusion assay and broth macro dilution method. Compounds 7a, 7e and 7g-h showed promising in vitro activity when tested against fungal pathogen Aspergillus niger whereas compounds 7e-h and 7j showed promising activity when tested against fungal pathogen Candida albicans. Compounds 7c and 7f showed potent inhibition against the growth of Gram negative bacteria Pseudomonas aeruginosa and compounds 7e, 7g-h and 7j inhibited the growth of tested Gram positive bacteria Bacillus subtilis and Staphylococcus aureus.