Palladium-Catalyzed Asymmetric (3 + 2) Cycloaddition of Vinyl Epoxides with Substituted Propiolates. Enantioselective Formation of 2,3,4-Trisubstituted 2,3-Dihydrofurans

BF3·OEt2 Catalyzed Cascade [4 + 2] Benzannulation of Vinyloxiranes with Coumarins to Construct Benzocoumarin Derivatives

A BF3·OEt2-catalyzed cascade cyclization reaction of vinyloxirane with coumarin is described, affording the benzocoumarin derivatives with moderate to excellent yields (72-92%). The reaction demonstrates exceptional substrate tolerance and has been extensively explored for its potential in drug development, including scale-up experiments, functional group transformations, and screening of the products for anticancer activity. Moreover, the reaction mechanism has been rigorously validated through intermediate trapping and control experiments. Additionally, this reaction represents the uncommon nonmetal catalyzed intermolecular cyclization of vinyloxiranes.

Recent updates on vinyl cyclopropanes, aziridines and oxiranes: access to heterocyclic scaffolds

This present review delineates the repertoire of vinyl cyclopropanes and their stuctural analogues to accomplish a wide array of oxa-cycles, aza-cycles, and thia-cycles under transition metal catalysis and metal-free approaches from early 2019 to the present date. The generation of electrophilic π-allyl intermediates and 1-3/1-5-dipolarophile chemistry originating from VCPs are always green, step- and atom-economical and sustainable strategies in comparsion with prefunctionalized and/or C-H activation protocols. Here, the strained ring-system extends its applicability by relieving the strain to undergo a ring-expansion reaction to accomplish 5-9 membered carbo- and heterocyclic systems. The availability of chiral ligands in the ring-expansion reaction of VCPs and their analogues has paved the way to realizing asymmetric synthetic transformations.

Lewis Acid-Catalyzed Benzannulation of Vinyloxiranes with 3-Formylchromones or 1,4-Quinones for Diversely Functionalized 2-Hydroxybenzophenones, 1,4-Naphthoquinones, and Anthraquinones

A facile and convenient protocol for the regioselective construction of functionalized 2-hydroxybenzophenones is described. This protocol involves the Sc(OTf)3/BF3·OEt2-catalyzed benzannulation of 2-vinyloxirans with 3-formylchromone, which involves cascade in situ diene formation, [4 + 2] cycloaddition, elimination, and ring-opening strategies. Moreover, it provides an expedited synthetic pathway to access biologically intriguing 1,4-naphthoquinones and anthraquinones including vitamin K3 and tectoquinone. The synthesized compounds also hold potential for use as UV filters and show promise as chemosensors for Cu2+ and Mg2+ ions.

Recent advances in Pd-catalyzed asymmetric cyclization reactions

Over the past few decades, there have been major developments in transition metal-catalyzed asymmetric cyclization reactions, enabling the convenient access to a wide spectrum of structurally diverse chiral carbo- and hetero-cycles, common skeletons found in fine chemicals, natural products, pharmaceuticals, agrochemicals, and materials. In particular, a plethora of enantioselective cyclization reactions have been promoted by chiral palladium catalysts owing to their outstanding features. This review aims to collect the latest advancements in enantioselective palladium-catalyzed cyclization reactions over the past eleven years, and it is organized into thirteen sections depending on the different types of transformations involved.

Intermolecular Carbophosphination of Alkynes with Phosphole Oxides via Ni-Al Bimetal-Catalyzed C-P Bond Activation

Intermolecular carbophosphination reaction of alkynes or alkenes with unreactive C-P bonds remains an elusive challenge. Herein, we used a Ni-Al bimetallic catalyst to realize an intermolecular carbophosphination reaction of alkynes with 5-membered phosphole oxides, providing a series of 7-membered phosphepines in up to 94 % yield.

Studies on the [4 + 2] cycloaddition and allylic substitution of indole-fused zwitterionic π-allylpalladium

The zwitterionic π-allylpalladium species, also known as dipoles, are important synthons widely used in various reactions including cycloaddition and allylic substitution. This study reported the development of a new indole-fused zwitterionic π-allylpalladium precursor compound and its application in [4 + 2] cycloaddition and allylic substitution reactions. As a result, the synthesis of pyrrolo[3,2,1-ij]quinazolin-3-one and 7-vinyl indole compounds was achieved with moderate to good yields. Notably, the allylic substitution reaction exhibited excellent regio- and stereoselectivity.

Asymmetric cascades of the π-allyl complex: a journey from transition-metal catalysis to metallaphotocatalysis

The enantioselective catalytic cascade involving Tsuji-Trost allylation has provided a viable strategy for the construction of multiple asymmetric C-C and C-X centres and numerous methods have been developed around it for the synthesis of various vital scaffolds. The synthetic utility of this strategy was enhanced by replacing the customary allyl acetates with ethylene diacetates/dicarbonates, vinyl epoxides, vinyl oxetanes, vinyl ethylene carbonates, vinyl cyclopropanes, enynes, and dienes using transition-metal catalysis. One more milestone was achieved when metallaphotocatalysis provided the necessary platform for these cascades by using a cheaper metal. This review will provide a summary of these enantioselective catalytic cascades from 2015.

Synthesis of Chiral 2,3-Dihydrofurans via One-Pot Pd-Catalyzed Asymmetric Allylic Cycloaddition and a Retro-Dieckmann Fragmentation Cascade

An efficient method for the enantioselective synthesis of 2,3-dihydrofurans bearing a quaternary stereocenter has been developed via Pd-catalyzed asymmetric allylic cycloaddition and a retro-Dieckmann Fragmentation cascade. The asymmetric allylic cycloaddition of vinylethylene carbonates with 3-cyanochromone followed by base-assisted retro-Dieckmann fragmentation proceeded smoothly via a one-pot process to produce chiral 3,4-disubstituted 2,3-dihydrofurans in high yields with excellent enantioselectivities.

Magnetic chitosan stabilized Cu(II)-tetrazole complex: an effective nanocatalyst for the synthesis of 3-imino-2-phenylisoindolin-1-one derivatives under ultrasound irradiation

In the present research, a recyclable catalyst has been prepared via a simple approach using chitosan as a linear polysaccharide. This paper reports the synthesis of novel copper(II) complex of 5-phenyl-1H-tetrazole immobilized on magnetic chitosan (MCS@PhTet@Cu(II)) as an effective catalyst. Transmission electron microscopy (TEM), field emission scanning electron microscopy (FESEM), vibrating sample magnetometer (VSM), Fourier-transform infrared spectroscopy (FT-IR), X-ray diffraction (XRD), energy-dispersive X-ray spectroscopy (EDS), and inductively coupled plasma mass spectrometry (ICP-MS) techniques were applied for the characterization of the catalyst. The catalytic activity of MCS@PhTet@Cu(II) was evaluated in the ultrasound-assisted synthesis of 3-imino-2-phenylisoindolin-1-one derivatives via the reaction between benzoyl chloride and arylcyanamides in ethanol at ambient temperature. Utilizing a wide variety of arylcyanamides under mild conditions, no use of toxic organic solvents, moderate reaction time, high yields along with catalyst excellent reusability and easy separation of the products without any tedious separation techniques, made this method a novel and simple process. The resulting heterogeneous catalyst showed valuable advantages such as easier work-up, better stability, and greater separation ability using an external magnet. The catalyst showed high efficacy and recyclability even after five cycles with no significant loss of its efficacy. The present methodology provides a path for the preparation of structurally diverse heterocyclic compounds, which may exhibit important biological activity.

Construction of nine-membered N,N,O-heterocycles via Pd-catalyzed [6+3] dipolar cycloaddition

A new approach for the synthesis of 9-membered N,N,O-heterocycles by Pd-catalyzed [6+3] dipolar cycloaddition of N-iminoisoquinolinium ylides and 2-vinyl oxetanes has been developed.

Chemoselective and diastereodivergent synthesis of new spirooxindolo-pyrrolizidines and pyrrolidines stemming from unsymmetrical 1,3-bis(arylidene)tetral-2-ones: a combined experimental and theoretical study

An experimental and theoretical study of an efficient one-pot three-components cycloaddition reaction leading to pentacyclic dispiropyrrolizidin/pyrrolidinoxindoles endowed by four contiguous stereogenic centres with moderate to good yields was reported.

Gold-catalyzed formal (3 + 2) and (4 + 2) cycloaddition reactions using propiolates: assembly of 2,3-dihydrofurans and 3,4-dihydropyrans via a multistep cascade process

A gold-catalyzed formal dipolar cycloaddition reaction was developed using polarized alkynes as dipolarophiles and butenediol or pentenediol derivatives as formal dipoles. Silyl groups were used to solve the selectivity issue of unsymmetrical diols.