Divergent Syntheses of Indoles and Quinolines Involving N1-C2-C3 Bond Formation through Two Distinct Pd Catalyses

One-Pot Three-Component Reaction for the Synthesis of 3,4-Dihydroquinazolines and Quinazolin-4(3H)-ones

A highly efficient and straightforward one-pot synthesis of diversely substituted 3,4-dihydroquinazolines and quinazolin-4(3H)-ones has been achieved through a domino three-component assembly reaction of arenediazonium salts, nitriles, and bifunctional aniline derivatives. This new protocol involves three C-N bond formations through the initial formation of N-arylnitrilium intermediates from arenediazonium salts and nitriles, followed by the sequential nucleophilic addition and cyclization reactions with bifunctional anilines, leading to such N-heterocyclic compounds of biological and pharmacological importance. This method offers a simple, expedient, and robust approach with the use of amenable and easily accessible reactants/reagents under metal-free mild conditions, good functional group tolerance, and high efficiency. The synthetic applications were also demonstrated by derivatization of the products obtained from these processes and syntheses of a diverse range of valuable polycyclic N-heterocycles.

Intramolecular CH-Hydrogen Bonding During the Dissociation of the Oxaphosphetane Intermediate Facilitates Z/E-Selectivity in Wittig Olefination

Herein, DFT studies corroborating experimental results revealed that the shortest intramolecular hydrogen bonding distance of cis/trans-oxaphosphetane (OPA) oxygen with the CH-hydrogen of a triphenylphosphine phenyl ring provides good evidence for the attained olefin Z/E-selectivity in Wittig olefination of the studied examples. 2-Nitrobenzaldehyde, 3-nitrobenzaldehyde, 2-nitro-3-bromobenzaldehyde, 2-nitro-5-bromobenzaldehyde and 2-nitro-5-arylbenzaldehydes provided Z-nitrostilbenes with (2-chloro-4-hydroxy-3-methoxy-5-(methoxycarbonyl)benzyl) triphenylphosphonium chloride as the major products. However, 4-nitrobenzaldehyde and 2-nitro-6-bromobenzaldehydes furnished E-nitrostilbenes as the major products in high yields. Furthermore, the DFT computed intramolecular CH1/CH2-hydrogen bond distances with Cl/NO2 of selected stilbene derivatives were in good agreement with intramolecular hydrogen bond distances measured from single-crystal X-ray diffraction measurements.

Simple Tandem Olefin Isomerization/Intramolecular Hydroamination of Alkenyl Amines with Various Allylic Tethers

A simple and efficient AgOTf-promoted tandem olefin isomerization/intramolecular hydroamination of 1,1-disubstituted alkenyl amines has been developed. This one-pot process represents a facile and attractive route for the synthesis of diverse 2-alkyl-substituted 1,3-X,N-heterocycles through chemo- and regioselective C(sp³)-N bond formation with atom economy. Advantages such as the operationally simple and practical procedure that uses a readily available catalyst under aerobic conditions, good to excellent chemical yields, the high functional group tolerance, the broad substrate scope, and high efficiency and selectivity are noteworthy.

HOAc catalyzed three-component reaction for the synthesis of 3,3'-(arylmethylene)bis(1H-indoles)

An efficient HOAc catalyzed three-component reaction of 2-(arylethynyl)anilines with arylaldehydes has been achieved, which leads to the generation of 3,3'-(arylmethylene)bis(1H-indoles) with good to excellent yields and high regioselectivity under transition-metal-free conditions. Four new C-C and C-N bonds were effectively formed in a one-pot procedure. Subsequent research on the reaction mechanism indicated that the reaction likely involved the processes of intramolecular cyclization and cascade intermolecular dehydration condensation.

An Oxidant- and Catalyst-Free Synthesis of Dibenzo[a,c]carbazoles via UV Light Irradiation of 2,3-Diphenyl-1H-indoles

An efficient methodology for the synthesis of dibenzo[a,c]carbazoles via annulation of 2,3-diphenyl-1H-indoles in EtOH under UV light irradiation (λ = 365 nm) along with hydrogen evolution is described. This method exhibits the advantages of mild reaction conditions, no requirement of any oxidants and catalysts, and release of hydrogen as the only byproduct. Notably, the mechanism investigation confirms that the trans-4b,8a-dihydro-9H-dibenzo[a,c]carbazole intermediate could convert into cis-4b,8a-dihydro-9H-dibenzo[a,c]carbazole, which relies on the nitrogen atom of the indole ring. This is followed by intramolecular dehydrogenation which yields the dibenzo[a,c]carbazoles.

Paired electrolysis enabled annulation for the quinolyl-modification of bioactive molecules

A paired electrolysis enabled cascade annulation that enables the efficient synthesis of highly functionalized quinoline-substituted bioactive molecules from readily available starting materials is reported. Using this methodology, two goals, namely, the direct synthesis of quinolines and the introduction of quinoline moieties to bioactive molecules, can be simultaneously achieved in one simple operation. The use of electroreduction for the activation of isatin, together with the further anodic oxidation of KI to catalytically result in a cascade annulation, highlight the unique possibilities associated with electrochemical activation methods. This transformation can tolerate a wide range of functional groups and can also be used as a functionalization tactic in pharmaceutical research as well as other areas.

Camphorsulfonic Acid-Mediated One-Pot Tandem Consecutive via the Ugi Four-Component Reaction for the Synthesis of Functionalized Indole and 2-Quinolone Derivatives by Switching Solvents

A camphorsulfonic acid-mediated one-pot tandem consecutive approach was developed to synthesize functionalized indole and 2-quinolone derivatives from the Ugi four-component reaction by switching solvents. A reaction of the Ugi adduct in an aprotic solvent undergoes 5-exo-trig cyclization to form an indole ring. In a protic solvent, however, the Ugi adduct undergoes an alkyne-carbonyl metathesis reaction to form a 2-quinolone ring.

Rhodium-Catalyzed Dehydrogenative Annulation of N-Arylmethanimines with Vinylene Carbonate for Synthesizing Quinolines

Here we report a novel Rh-catalyzed C-H/C-H alkenylation of N-arylmethanimines with vinylene carbonate acting as a vinylene unit. Forty examples of C3,C4-nonsubstituted quinolines were achieved from commercially available starting materials. This identified process features an exceedingly simple system, a lower loading of catalyst, and the capacity for postfunctionalization with bioactive molecules.

Metal-Promoted Heterocyclization: A Heterosynthetic Approach to Face a Pandemic Crisis

The outbreak of SARS-CoV-2 has drastically changed our everyday life and the life of scientists from all over the world. In the last year, the scientific community has faced this worldwide threat using any tool available in order to find an effective response. The recent formulation, production, and ongoing administration of vaccines represent a starting point in the battle against SARS-CoV-2, but they cannot be the only aid available. In this regard, the use of drugs capable to mitigate and fight the virus is a crucial aspect of the pharmacological strategy. Among the plethora of approved drugs, a consistent element is a heterocyclic framework inside its skeleton. Heterocycles have played a pivotal role for decades in the pharmaceutical industry due to their high bioactivity derived from anticancer, antiviral, and anti-inflammatory capabilities. In this context, the development of new performing and sustainable synthetic strategies to obtain heterocyclic molecules has become a key focus of scientists. In this review, we present the recent trends in metal-promoted heterocyclization, and we focus our attention on the construction of heterocycles associated with the skeleton of drugs targeting SARS-CoV-2 coronavirus.

Copper(ii) triflate catalyzed three-component reaction for the synthesis of 2,3-diarylquinoline derivatives using aryl amines, aryl aldehydes and styrene oxides

An efficient and expedient synthetic protocol is reported for the synthesis of 2,3-diarylquinoline derivatives from readily available aryl amines, aryl aldehydes and styrene oxides using 10 mol% copper(ii) triflate by employing three-component reaction.