Competing Domino Knoevenagel-Cyclization Sequences with N-Arylcinnamylamines

Domino Knoevenagel-cyclization reactions of N-arylcinnamylamines were carried out with active methylene reagents, which took place with five competing cyclization mechanisms: intramolecular hetero Diels-Alder reaction, stepwise polar [2 + 2] cycloaddition, styryl or aza-Diels-Alder reactions followed by rearomatization, and [1,5]-hydride shift-6-endo cyclization. In the stepwise aza-Diels-Alder reaction, the N-vinylpyridinium moiety acted as an azadiene, producing a condensed heterocycle with tetrahydroquinolizinium and tetrahydroquiniline subunits. Antiproliferative activity with low micromolar IC50 values was identified for some of the novel scaffolds.

A triple cascade approach towards the diastereoselective synthesis of spiro trans-decalinol scaffolds

A [2+2+2] annulation reaction between cyclohexanone, β-nitrostyrene and 2-arylidene-1,3-indanedione afforded multisubstituted spiro trans-decalinol derivatives in high chemical yields (up to 75%) and excellent diastereoselectivity (up to >20 : 1) at room temperature. This one-pot three-component system follows a triple cascade sequence via the Michael/nitro-Michael/Aldol process, resulting in the formation of three C-C bonds, five contiguous stereocenters as well as a spiro quaternary carbon center.

Construction of hybrid polycyclic quinolinobenzo[a]phenazinone architectures using solid-state melt reaction (SSMR)

An efficient and versatile protocol for the synthesis of hybrid polycyclic quinolinobenzo[a]phenazinones has been developed under SSMR condition via intramolecular domino Knoevenagel-hetero-Diels-Alder reaction involving the generation of two new six membered fused rings and three contiguous stereogenic centers.

Domino ring opening and selective O/S-alkylation of cyclic ethers and thioethers

Chemoselective domino ring opening and selective O/S-alkylation of ethers/thioethers over enol C/O alkylation has been observed. Various 2-aryl chromanones/thiochromanones with alkyl/allyl bromides were smoothly converted into the corresponding highly functionalized ethers and thioethers in excellent yields with high selectivity. An unusual, chemoselective domino ring opening and selective ether/thioether O/S-alkylation over. An unusual, chemoselective domino ring opening and selective ether/thioether O/S alkylation over enol C/O alkylation has been observed.

Intramolecular [3 + 2] nitrone cycloaddition reaction: highly regio and diastereoselective synthesis of bicyclo[3.2.1]octane scaffolds

A regio and diastereoselective strategy has been developed for the synthesis of complex bicyclo[3.2.1]octane scaffolds from the reaction of readily accessible vinylogous carbonates with N-substituted hydroxylamine hydrochlorides via intramolecular 1,3-dipolar nitrone cycloaddition reaction. Wide varieties of bicyclic isoxazolidines were synthesized in high yields under catalyst free conditions through a highly efficient and operationally simple protocol.

An expedient, one-pot, stepwise sequential approach for the regioselective synthesis of pyrazolines

An efficient approach for the synthesis of pyrazoline/pyrazole-tethered pyridinyl methanones is described via a one-pot, stepwise, sequential methodology using chalcones and pyridine-4-carbohydrazide as substrates through a Michael addition followed by cyclization. The reaction proceeds via a catalyst-, solvent-, work-up-, and column-chromatography-free method under melt conditions to provide the pyrazolines in short reaction times with high atom efficiency.

Rhodium-Catalyzed Diastereoselective [3 + 2] Cycloaddition of Carbonyl Ylide: An Access to the Core Ring System of Cordigol and Lophirone H

This paper describes a new synthetic strategy for the construction of tricyclic chromeno/quinolino furan frameworks via creation of two new rings and three contiguous stereogenic centers with high diastereoselectivity through a rhodium-catalyzed intramolecular carbonyl ylide cycloaddition reaction for the first time. This protocol allows the synthesis of the core ring system of natural products such as cordigol and lophirone H.

Ruthenium-catalyzed, site-selective C-H activation: access to C5-substituted azaflavanone

A site-selective ruthenium-catalyzed keto group assisted C–H bond activation of 2-aryl tetrahydroquinoline (azaflavanone) derivatives has been achieved with a variety of alkenes for the first time. A wide range of substrates was utilized for the synthesis of a wide variety of alkenylated azaflavanones. This simple and efficient protocol provides the C5-substituted azaflavanone derivatives in high yields with a broad range of functional group tolerance. Further, the C5-alkenylated products were converted into substituted 2-aryl quinoline derivatives in good yields.

A site-selective ruthenium-catalyzed keto group assisted C–H bond activation of 2-aryl tetrahydroquinoline (azaflavanone) derivatives has been achieved with a variety of alkenes for the first time.

Highly efficient catalyst-free domino conjugate addition, decarboxylation and esterification/amidation of coumarin carboxylic acid/esters with pyrazolones: a green chemistry approach

Tandem conjugate addition, decarboxylation and esterification/amidation of coumarin 3-carboxylic acid derivatives with pyrazolones have been developed.

Cascade annulation reaction (CAR): highly diastereoselective synthesis of pyranopyrazole scaffolds

An unprecedented domino protocol for the novel synthesis of highly diverse and functionalized tetrahydro pyranopyrazole scaffolds using chalcone epoxide has been reported for the first time. This synthetic protocol generates three consecutive stereogenic centres in a highly diastereoselective manner with the formation of vicinal diol and a quaternary carbon centre. A wide range of substrates were utilized for the scope of this methodology and provided very good yields of pyranopyrazoles. The pyranopyrazoles were also transformed into densely functionalized tetrasubstituted olefins.

An unprecedented domino protocol for the novel synthesis of highly diverse and functionalized tetrahydro pyranopyrazole scaffolds using chalcone epoxide has been reported.

Two step, one-pot sequential synthesis of functionalized hybrid polyheterocyclic scaffolds via a solid state melt reaction (SSMR)

A new one pot assembly of highly functionalized benzo[a]phenazinone fused chromene/bicyclic scaffolds via a domino Knoevenagel intramolecular hetero-Diels-Alder (IMHDA) strategy using a solid state melt reaction (SSMR) of 2-hydroxynaphthalene 1,4-dione, o-phenylenediamine, O-allyl salicylaldehyde/O-vinyl salicylaldehyde derivatives is reported. The formation of five new bonds (two C-C bonds and three C-O bonds), three six-membered rings, and three stereogenic centers in a one-pot manner is very attractive. Ease of reaction with short time, good yields with water as the only byproduct and work up free procedure are some of the excellent features of the present protocol.

A novel multicomponent quadruple/double quadruple domino reaction: highly efficient synthesis of polyheterocyclic architectures

A novel multicomponent quadruple domino reaction (MCQDR) for the assembly of structurally complex molecular architectures via the formation of three rings and three contiguous stereogenic centers has been accomplished with high regio- and diastereoselectivity. Solvents, catalysts and work-up were not required to obtain the target molecules. In addition, this new protocol is also extended for the multicomponent double quadruple domino reaction (MCDQDR) to create novel polyheterocyclic architectures in an orthogonal manner.

A rearrangement involving a solid-state melt reaction for the synthesis of multifunctional tetrasubstituted olefins

A new catalyst- and solvent-free intramolecular rearrangement sequence leading towards benzimidazole-tethered tetrasubstituted olefins through a solid-state melt reaction (SSMR).

Ruthenium catalyzed chemo and site-selective C–H amidation of oxobenzoxazine derivatives with sulfonyl azides

A novel and general protocol towards the synthesis of highly functionalized ortho-amido oxobenzoxazine frameworks via ruthenium catalyzed intermolecular C–H amidation using sulfonyl azides as amidation components has been developed for the first time.

A distal vinyl shift (DVS) through quadruple domino reaction: synthesis of N-vinyl benzoheterocyclic scaffolds

An unprecedented Distal Vinyl Shift (DVS) through quadruple domino reaction has been disclosed via the synthesis of N-vinyl benzoheterocyclic scaffolds.

Solvent and catalyst free ring expansion of indoles: a simple synthesis of highly functionalized benzazepines

Highly functionalized benzazepines have been synthesized from indoles via ring expansion. Ring contraction of benzazepines to indole derivatives has also been acheived in excellent yields.

Intramolecular Diaza-Diels-Alder Protocol: A New Diastereoselective and Modular One-Step Synthesis of Constrained Polycyclic Frameworks

Phenotype-based screening of diverse compound collections generated by privileged substructure-based diversity-oriented synthesis (pDOS) is considered one of the prominent approaches in the discovery of novel drug leads. However, one key challenge that remains is the development of efficient and modular synthetic routes toward the facile access of privileged small-molecule libraries with skeletal and stereochemical complexity and drug-like properties. In this regard, a novel and diverse one-pot procedure for the diastereoselective synthesis of privileged polycyclic benzopyrans and benzoxepines is described herein. These unexplored chemotypes were accessed by utilizing an acid-mediated diaza-Diels-Alder reaction of 2-allyloxy- and/or homoallyloxy benzaldehyde with 2-aminoazine building blocks. Profiling of representative analogues against blood-stage Plasmodium falciparum parasites identified three lead candidates with low micromolar antimalarial activity.

Highly regio- and diastereo-selective synthesis of novel tri- and tetra-cyclic perhydroquinoline architectures via an intramolecular [3 + 2] cycloaddition reaction

A facile and efficient synthetic protocol was established for the construction of novel tri- and tetra-cyclic pyrrolo/pyrrolizinoquinoline architectures via the in situ formation of azomethine ylide followed by an intramolecular [3 + 2] cycloaddition reaction strategy. This protocol leads to the creation of two/three new rings and three/four contiguous stereocentres, in which one of them is a tetra-substituted carbon center, in a highly diastereoselective fashion with excellent yields.

Stereoselective construction of functionalized tetracyclic and pentacyclic coumarinopyranpyrazole/pyrimidinedione/coumarin scaffolds using a solid-state melt reaction

An assembly of tetra / pentacyclic hybrid scaffolds have been synthesized for the first time using a solid-state melt reaction in a stereoselective fashion with excellent yields.

A novel protocol for the facile construction of tetrahydroquinoline fused tricyclic frameworks via an intramolecular 1,3-dipolar nitrile oxide cycloaddition reaction

An efficient method towards the synthesis of quinoline fused tricyclic compounds involving an intramolecular 1,3-dipolar nitrile oxide cycloaddition reaction utilizing Baylis–Hillman derivatives in good yields has been described for the first time.

A novel, facile, rapid, solvent free protocol for the one pot green synthesis of chromeno[2,3-d]pyrimidines using reusable nano ZnAl2O4– a NOSE approach and photophysical studies

The preparation of an eco-friendly, highly stable, reusable nano ZnAl₂O₄was used as an excellent catalyst for the pseudo four component synthesis of a library of fluorescent chromeno[2,3-d]pyrimidine derivatives.

A domino synthetic approach for new, angular pyrazol- and isoxazol-heterocycles using [DBU][Ac] as an effective reaction medium

Some new, angular pyrazol- and isoxazol-heterocycles have been synthesized by the reaction of pyrazolone/isoxazolone with typical ketone-based substrates—O-alkenyloxy/alkynyloxy-acetophenones.

A facile synthesis of isoxazolo[3,4-a]pyrrolizine and isoxazolo[4,3-c]pyridine derivatives via intramolecular nitrone cycloaddition reaction

Isoxazolo [3,4-a]pyrrolizine and isoxazolo[4,3-c]pyridine are formed by a facile and efficient intramolecular [3 + 2] nitrone cycloaddition, forming two new rings and three contiguous stereocentres with high diastereoselectivity and good yields.

Synthesis of highly diversified 1,2,3-triazole derivatives via domino [3 + 2] azide cycloaddition and denitration reaction sequence

Synthesis of 1,2,3-triazoles via domino azide cycloaddition and denitration reaction sequence under catalyst free conditions is described. Sodium azide treatment of Baylis–Hillman adducts and their cyclic derivatives from nitro olefins gave the triazoles in excellent yield.