Polycyclic Pyrazolidines by Tandem Diazomalonate Dipolar Cycloadditions and CpRu-Catalyzed Carbene Additions

Thanks to the ability of diazo derivatives to react either as 1,3-dipoles and as carbenes after dinitrogen extrusion, combinations of oxa or aza benzonorbornadienes and diazomalonates afford polycyclic pyrazolidines via a three-step sequence of (i) a highly diastereoselective [3+2]-cycloaddition, (ii) a CpRu-catalyzed carbene addition, and (iii) a second dipolar cycloaddition. Of importance, step (II) represents a unique access to novel bench-stable N,N-cyclic azomethine imines, which behave as effective 1,3-dipoles in combination with electron-poor dipolarophiles. Each step proceeds efficiently and the 3-step process can be performed in one-pot to yield a polycyclic pyrazolidine in excellent overall yield (90 %).

Different routes for the construction of biologically active diversely functionalized bicyclo[3.3.1]nonanes: an exploration of new perspectives for anticancer chemotherapeutics

Cancer is the second most high-morbidity disease throughout the world. From ancient days, natural products have been known to possess several biological activities, and research on natural products is one of the most enticing areas where scientists are engrossed in the extraction of valuable compounds from various plants to isolate many life-saving medicines, along with their other applications. It has been noticed that the bicyclo[3.3.1]nonane moiety is predominant in most biologically active natural products owing to its exceptional characteristics compared to others. Many derivatives of bicyclo[3.3.1]nonane are attractive to researchers for use in asymmetric catalysis or as potent anticancer entities along with their successful applications as ion receptors, metallocycles, and molecular tweezers. Therefore, this review article discusses several miscellaneous synthetic routes for the construction of bicyclo[3.3.1]nonanes and their heteroanalogues in association with the delineation of their anticancer activities with few selective compounds.

Copper-Catalyzed Cycloadditions of Diazo Compounds with Imidazolidines/Hexahydropyrimidines for the Syntheses of N-Heterocycles

Reported herein are the unprecedented copper-catalyzed formal [n + 1]/[n + 3] (n = 5, 6) cycloadditions of diazo compounds with imidazolidines/hexahydropyrimidines, thus providing a general, economical, and efficient route to construct different sized (six- to nine-membered) diaza-heterocycles in moderate to excellent yields under mild reaction conditions. This strategy features the use of copper catalyst to accomplish such diverse annulations and the utilization of imidazolidines/hexahydropyrimidines as stable 1,5-/1,6-dipoles.

Biocatalytic One-Carbon Ring Expansion of Aziridines to Azetidines via a Highly Enantioselective [1,2]-Stevens Rearrangement

We report enantioselective one-carbon ring expansion of aziridines to make azetidines as a new-to-nature activity of engineered "carbene transferase" enzymes. A laboratory-evolved variant of cytochrome P450_BM3, P411-AzetS, not only exerts unparalleled stereocontrol (99:1 er) over a [1,2]-Stevens rearrangement but also overrides the inherent reactivity of aziridinium ylides, cheletropic extrusion of olefins, to perform a [1,2]-Stevens rearrangement. By controlling the fate of the highly reactive aziridinium ylide intermediates, these evolvable biocatalysts promote a transformation which cannot currently be performed using other catalyst classes.

A nitrogen-based chiral catenane for enantioenriching photocatalytic aerobic oxidation

Tröger's base's chirality merges catenanes’ photosensitizing characteristics to introduce the first nitrogen-based chiral hetero[2]catenane that proceeds enantioenriching photocatalytic aerobic oxidations.

Optically active and photoswitchable Tröger's base analogs

Azo carrying Tröger's base analogs introduced chirality, thermochromic and phototunable properties to an achiral liquid crystal host.

Polycyclic Indoline-Benzodiazepines through Electrophilic Additions of α-Imino Carbenes to Tröger Bases

Polycyclic indoline-benzodiazepines can be accessed through the intermolecular reaction of Tröger bases with N-sulfonyl-1,2,3-triazoles. Under RhII catalysis, α-imino carbenes are generated and a subsequent cascade of [1,2]-Stevens, Friedel-Crafts, Grob, and aminal formation reactions yield the polycyclic heterocycles as single isomers (d.r.>49:1, four stereocenters including two bridgehead N atoms). Further ring expansion by insertion of a second α-imino carbene leads to elaborated polycyclic 9-membered-ring triazonanes.

Synthesis of 6,12-Epiminodibenzo[b,f][1,5]diazocines via an Ytterbium Triflate-Catalyzed, AB2 Three-Component Reaction

An efficient and selective procedure for the synthesis of epiminodibenzo[b,f][1,5]diazocines involving a AB₂ three-component reaction is developed. Two equivalents of suitably substituted 2-aminoarylaldehydes reacted with arylamines in the presence of Yb(OTf)₃ to afford the desired products in high yields. The reaction is highly atom-economic and waste-free, in addition to allowing the generation of two heterocyclic rings and four C-N bonds in a single operation. Significantly, this approach is complementary to the existing literature procedures, affording arylamine-derived products that could not be accessed previously. A plausible mechanism is proposed involving an imine formation-intermolecular annulation-intramolecular iminium ion cyclization sequence.

Accessing N-Stereogenicity through a Double Aza-Michael Reaction: Mechanistic Insights

Further development of the chemistry and applications of chiral compounds that possess configurationally stable stereogenic nitrogen atoms is hampered by the lack of efficient strategies to access such compounds in an enantiomerically pure form. Esters of propiolic acid and chiral alcohols were evaluated as cheap and readily available Michael acceptors in a diastereoselective synthesis of N-stereogenic compounds by means of a double aza-Michael conjugate addition. Diastereomeric ratios of up to 74:26 and high yields were achieved with (-)-menthyl propiolate as a substrate. Furthermore, a detailed mechanistic investigation was undertaken to shed some light on the course of this domino transformation. Kinetic studies revealed that the protic-solvent additive acts as a Brønsted acid and activates the ester toward the initial attack of the tetrahydrodiazocine partner. Conversely, acidic conditions proved unfavorable during the final cyclization step that provides the product.

Copper(i) catalyzed diastereoselective multicomponent synthesis of spiroindolo-pyrrolidines/-imidazolidines/-triazolidines from diazoamides via azomethine ylides

Investigations of stereoselective studies on three-/four-component reactions in the presence of copper(i) thiophene-2-carboxylate as a catalyst are performed to afford spiroindolo-pyrrolidines/-imidazolidines/-triazolidines in good yields.

Diastereoselective three-component synthesis of β-amino carbonyl compounds using diazo compounds, boranes, and acyl imines under catalyst-free conditions

Diazo compounds, boranes, and acyl imines undergo a three-component Mannich condensation reaction under catalyst-free conditions to give the anti β-amino carbonyl compounds in high diastereoselectivity. The reaction tolerates a variety of functional groups, and an asymmetric variant was achieved using the (−)-phenylmenthol as chiral auxiliary in good yield and selectivity. These β-amino carbonyl compounds are valuable intermediates, which can be transformed to many potential bioactive molecules.