Synthesis of Bridged Five-Membered Ring Systems by Type II [3 + 2] Annulation of Allenylsilane-ene

The first type II intramolecular [3 + 2] annulation of allenylsilane-ene has been achieved, enabling diastereoselective and efficient construction of synthetically challenging bridged five-membered ring systems such as bicyclo[3.2.1]. This mild and direct process shows a broad substrate scope and is highly stereospecific. Particularly, this work represents the first stereoselective method for the direct synthesis of bicyclo[3.2.1] ring systems from acyclic precursors. Additionally, the first asymmetric total syntheses of (+)- and (-)-strepsesquitriol, and the efficient formation of the synthetically challenging tetracyclic core of pierisjaponol D are achieved by this type II [3 + 2] annulation reaction.

Construction of Vicinal Quaternary Centers via Ru-Catalyzed Enantiospecific Allylic Substitution with Lithium Ester Enolates

The installation of vicinal quaternary centers with absolute stereocontrol constitutes a considerable challenge in organic synthesis. Herein, we introduce a novel [Cp*Ru(MeCN)3]PF6/phenoxythiazoline catalyst system that achieves enantiospecific allylic substitution of tertiary carbonates with α,α-disubstituted lithium ester enolates to give products containing vicinal quaternary centers. Noteworthy features include the direct use of nonstabilized ester enolates, a class of nucleophiles which has rarely been used in transition metal-catalyzed allylic substitution reactions. The approach is demonstrated for a broad scope of tertiary electrophiles as well as ester enolates and accomplishes stereoretentive substitution with excellent conservation of ee (89-99%) and branched/linear regioselectivities (up to 40:1).

Asymmetric 1,2-Migration at Vicinal Tetrasubstituted Stereocenters Constructed from α-Keto Imines

A carbonyl-assisted asymmetric 1,2-migratory allylation through in situ generation of vicinal tetrasubstituted stereocenters is reported to access enantiopure α-amino ketones and amino alcohols with excellent yields and diastereoselectivities. In a remarkable divergence, despite higher steric hindrance, the allylation exclusively occurs on ketones over imines in the first step, followed by a face-selective 1,2-allyl transfer, thus highlighting an exciting interplay between two distinct electrophiles. The methodology distinguishes itself through its adaptability to gram-scale synthesis, showcasing broad functional-group tolerance and stereodivergence. Density functional theory (DFT) analysis led to a deeper understanding of its selectivity and mechanistic framework. Highlighting its transformative potential, the method was applied to the total synthesis of hapalindole alkaloids.

Phosphine-Catalyzed Synthesis and Cytotoxic Evaluation of Michael Adducts of the Sesquiterpene Lactone Arglabin

A general method for chemo- and diastereoselective modification of anticancer natural product arglabin with nitrogen- and carbon-centered pronucleophiles under the influence of nucleophilic phosphine catalysts was developed. The locked s-cis-geometry of α-methylene-γ-butyrolactone moiety of arglabin favors for the additional stabilization of the zwitterionic intermediate by electrostatic interaction between phosphonium and enolate oxygen centers, leading to the unprecedentedly high efficiency of the phosphine-catalyzed Michael additions to this sesquiterpene lactone. Using n-Bu3P as the catalyst, pyrazole, phthalimide, 2-oxazolidinone, 4-quinazolinone, uracil, thymine, cytosine, and adenine adducts of arglabin were obtained. The n-Bu3P-catalyzed reaction of arglabin with active methylene compounds resulted in the predominant formation of bisadducts bearing a new quaternary carbon center. All synthesized Michael adducts and previously obtained phosphorylated arglabin derivatives were evaluated in vitro against eleven cancer and two normal cell lines, and the results were compared to those of natural arglabin and its dimethylamino hydrochloride salt currently used as anticancer drugs. 2-Oxazolidinone, uracil, diethyl malonate, dibenzyl phosphonate, and diethyl cyanomethylphosphonate derivatives of arglabin exhibited more potent antiproliferative activity towards several cancer cell lines and lower cytotoxicity towards normal cell lines in comparison to the reference compounds, indicating the feasibility of the developed methodology for the design of novel anticancer drugs with better therapeutic potential.

Asymmetric Carbene Transformations for the Construction of All-Carbon Quaternary Centers

Asymmetric catalytic carbene reactions have been well documented in the last few decades for the expeditious assembly of chiral molecules with structural diversity. However, the enantioselective construction of all-carbon quaternary centers remains a challenge in this area. In this review article, two types of asymmetric carbene reactions that beyond cyclopropanation, cyclopropenation, and Büchner reaction, have been summarized for the construction of all-carbon quaternary centers: 1) using carbene species as a 1C synthon that reacts with a trisubstituted prochiral center; 2) sequential installation of two different C-C bonds on the carbene position, which features a gem-difunctionalization reaction. Especially, the asymmetric metal carbene gem-dialkylation process, which has emerged as a practical and versatile method for the expeditious assembly of complex architectures from readily available chemical resources, is a complementary approach for the expeditious assembly of all-carbon quaternary centers.

Catalytic Asymmetric Synthesis of Vicinal Quaternary Stereocenters Enabled by Alkylation of α,α-Disubstituted Aldehydes with 3-Bromooxindoles

An organocatalytic enantioselective alkylation of α,α-disubstituted aldehydes with 3-bromooxindoles is reported. Enantioenriched oxindoles with vicinal quaternary stereocenters are accessed by an asymmetric conjugate addition process of branched aldehydes with o-azaxylylene intermediates (indol-2-ones). Key to the success of highly diastereo- and enantioselective transformations is the combined use of a triphenylsilyl-protected β-amino alcohol catalyst derived from the spiropyrrolidine scaffold and 3,5-dinitrobenzoic acid. This study also presents a rare example of aldehyde alkylation with the formation of consecutive quaternary stereocenters.

Function-Oriented Synthesis of Pentacyclic Triterpenoids and Discovery of an ent-Estrane as a Natural Product-Inspired Androgen Receptor Antagonist

While pentacyclic triterpenoids have a rich history in chemistry and biology, the challenges associated with their asymmetric synthesis contribute to the current reality that medicinal exploration in the area is largely constrained to natural product derivatization. To address this deficiency, a function-oriented synthesis of pentacyclic triterpenoids was pursued. Overall, we report a divergent synthesis of 26-norgermanicol and 26-norlupeol and we have identified a new class of androgen receptor antagonist that is ∼6× more potent than lupeol.

Total Synthesis of Putative Melognine

Total synthesis of melognine was accomplished. A 10-membered cyclic alkyne was prepared via an intramolecular SN2 reaction of a nosylamide. Enyne metathesis of the cyclic alkyne under an atmosphere of ethylene afforded a 1,3-diene. Intramolecular cycloaddition of a nitrone and an azomethine ylide with the 1,3-diene moiety constructed the characteristic highly fused skeleton. Further transformation, including ring-closing metathesis, resulted in the synthesis of melognine, whose NMR spectra did not match the reported data. Close inspection of the spectra of melognine in the literature suggested that the structure of melognine might be identical with that of a known alkaloid, melodinine L.

Total Synthesis of (+)- and (-)-Calycanthine by Means of Thio-Urea-Catalyzed Sequential Michael Reactions of Bis-oxindoles

A unified catalytic asymmetric approach to naturally occurring piperidinoindoline and pyrrololidinoindoline alkaloids has been realized via the development of a thio-urea-catalyzed sequential Michael addition of bis-oxindole onto nitroethylene (up to 93% ee and >20:1 dr). This strategy offers the total syntheses of either enantiomers of naturally occurring calycanthine.

Substrate-directed divergent annulations of sulfur ylides: synthesis of functionalized bispirocyclopentane and bispirocyclopropane derivatives

Herein, an efficient, substrate-directed divergent [2 + 3]/[2 + 1] annulation of tetra-substituted oxa-dienes and allylic sulfur ylides has been successfully developed. Under precise annulation regulation, a series of functionalized bispirocyclopentane and bispirocyclopropane derivatives were synthesized in a highly stereoselective and economical manner (up to 95% yield, >20 : 1 dr or >20 : 1 E/Z). This protocol offers the advantages of mild conditions, high chemo-, regio- and diastereoselectivity and broad substrate compatibility. In addition, the synthetic practicality of this protocol was evaluated through a scale-up preparation and a series of three-component reactions utilizing in situ generated sulfur ylides.

Progress Toward the Asymmetric De Novo Synthesis of Limonoids

Asymmetric de novo construction of limonoids remains a challenging problem in stereoselective synthesis due to the diverse and complex structures associated with this class of natural products. Here, a unique synthetic pathway to an "intact" limonoid system is described. The synthetic route is based on exploiting an oxidative rearrangement reaction of a densely functionalized late-stage intermediate to simultaneously establish the stereodefined C10 quaternary center and an allylic acetate at C12. This is a unique example of a complex rearrangement reaction that proceeds on a system whose presumed intermediate allyl cation is highly hindered and lacks neighboring protons that are otherwise required for cation termination.

Hydrated [3+2] Cyclotelomerization of Butafulvenes to Create Multiple Contiguous Fully Substituted Carbon Centers

The construction of multiple continuous fully substituted carbon centers, which serve as unique structural motif in natural products, is a challenging topic in organic synthesis. Herein, we report a hydrated [3+2] cyclotelomerization of butafulvenes to create contiguous fully substituted carbon backbone. In the presence of scandium triflate, all-carbon skeleton with spiro fused tricyclic ring can be constructed in high diastereoselectivity by utilizing butafulvene as the synthon. Mechanistic studies suggest that this atom-economic reaction probably proceeds through a synergistic process containing butafulvenes dimerization and nucleophilic attack by water. In addition, the tricyclic product can undergo a series of synthetic derivatizations, which highlights the potential applications of this strategy. The recyclability of Sc(OTf)3 has also been demonstrated to show its robust performance in this hydrated cyclotelomerization.

Catalytic enantioselective reductive Eschenmoser-Claisen rearrangements

An important challenge in enantioselective catalysis is developing strategies for the precise synthesis of neighboring congested all-carbon quaternary stereocenters. The well-defined transition states of [3,3]-sigmatropic rearrangements and their underlying stereospecificity render them powerful tools for the synthesis of such arrays. However, this type of pericyclic reaction remains notoriously difficult to catalyze, especially in an enantioselective fashion. Herein, we describe an enantioselective reductive Eschenmoser-Claisen rearrangement catalyzed by chiral 1,3,2-diazaphospholene-hydrides. This developed transformation enables full control of the two newly formed acyclic stereogenic centers, leading to amides with vicinal all-carbon quaternary-tertiary or quaternary-quaternary carbon atoms.

Vicinal All-Carbon Quaternary Stereocenter Construction with Trifluoromethyl Groups via Organocatalytic Asymmetric Cascade Michael/Michael Reaction

A thiourea organocatalyst efficiently promoted the asymmetric cascade Michael/Michael reactions between isatin-derived trifluoromethylacrylate and α-alkylidene succinimide, resulting in high yields of spirooxindole derivatives. These compounds exhibit vicinal all-carbon quaternary stereocenters and bear a trifluoromethyl group, with excellent enantioselectivities reaching up to 99 % ee. This work represents the first successful organocatalyst application for the direct construction of vicinal all-carbon quaternary stereocenters, featuring a trifluoromethyl group.

Enantioselective Total Syntheses of (-)-Caulamidine D and (-)-Isocaulamidine D and Their Absolute Configuration Reassignment

The first enantioselective total syntheses of (-)-caulamidine D (5) and (-)-isocaulamidine D (6) were accomplished. Their absolute configurations were unambiguously elucidated through X-ray crystallography. The isolated natural samples of both 5 and 6 are determined to be the TFA salts instead of the neutral forms. It took 16 steps (longest linear sequence) to divergently access both 5 and 6 following a unified strategy. The key reactions include (1) development and application of an asymmetric Meerwein-Eschenmoser-Claisen rearrangement to construct the challenging C10, C23 consecutive stereocenters and (2) application of a cascade 6-exo-dig/6-exo-tet amine/nitrile cyclization reaction.

Enantioselective [3+2]-cycloaddition of 2,3-disubstituted cyclobutenones: vicinal quaternary stereocenters construction and skeletal functionalization

Cycloaddition is a fundamental transformation, featuring the assembly of complex cyclic molecules with multiple stereocenters. We report here a silver-catalyzed [3+2]-cycloaddition of 2,3-disubstituted cyclobutenones with an array of azomethine ylide precursors iminoesters, furnishing azabicycles in good yields and enantioselectivities. Up to three contiguous all-carbon quaternary centers, including two angular stereocenters, could be constructed efficiently, due to high reactivity of strained cyclobutenones. Subsequent skeletal remodeling provided versatile molecules with distinct structural characters.

Anion-accelerated asymmetric Nazarov cyclization: access to vicinal all-carbon quaternary stereocenters

We have developed a catalytic asymmetric Nazarov cyclization that results in the formation of two contiguous all-carbon quaternary stereocenters in high yield with excellent levels of asymmetric induction. This method requires no catalyst recognition elements in the starting materials that are simple diketoesters. Geometrically pure E or Z isomers of the starting material lead to diastereomerically pure products with high enantioselectivity because the species that undergoes cyclization is a rhodium enolate that is configurationally stable.

Regiodivergent (3 + 2) annulation reactions of oxyallyl cations

We report a new method for the regiodivergent dearomative (3 + 2) reaction between 3-substituted indoles and oxyallyl cations. Access to both regioisomeric products is possible and is contingent on the presence or absence of a bromine atom on the substituted oxyallyl cation. In this way, we are able to prepare molecules that contain highly-hindered, stereodefined, vicinal, quaternary centers. Detailed computational studies employing energy decomposition analysis (EDA) at the DFT level establishes that regiochemical control arises from either reactant distortion energy or orbital mixing and dispersive forces, depending on the oxyallyl cation. Examination of the Natural Orbitals for Chemical Valence (NOCV) confirms that indole acts as the nucleophilic partner in the annulation reaction.

Total Synthesis of (±)- and (-)-Daphnillonin B

The first total synthesis of (±)- and (-)-daphnillonin B, a daphnicyclidin-type alkaloid with a new [7-6-5-7-5-5] A/B/C/D/E/F hexacyclic core, has been achieved. The [6-5-7] B/C/D ring system was efficiently and diastereoselectively constructed via a mild type I intramolecular [5+2] cycloaddition, followed by a Grubbs II catalyst-catalyzed radical cyclization. The [5-5] fused E/F ring system was synthesized via a diastereoselective intramolecular Pauson-Khand reaction. Notably, the synthetically challenging [7-6-5-7-5-5] hexacyclic core was reassembled by a unique Wagner-Meerwein-type rearrangement from the [6-6-5-7-5-5] hexacyclic framework found in calyciphylline A-type Daphniphyllum alkaloids.

Copper (I) Chloride-Catalyzed Photoredox Synthesis of Multifunctionalized Compounds at Room Temperature and Their Antifungal Activities

A simple visible-light-induced CuCl-catalyzed synthesis was developed for highly functionalized carbon-centered compounds (α-alk/aryloxy-α-diaryl/alkylaryl-acetaldehydes/ketones) at room temperature using benzoquinone, alkyl/aryl alcohol, and alkyl/aryl terminal/internal alkynes. Late-stage functionalized compounds show good antifungal activities, especially against Candida krusei fungal strain, in in vitro experiments (the Broth microdilution method). Moreover, toxicity tests (zebrafish egg model experiments) indicated that these compounds had negligible cytotoxicity. The green chemistry metrics (E-factor value is 7.3) and eco-scale (eco-scale value is 58.8) evaluations show that the method is simple, mild, highly efficient, eco-friendly, and environmentally feasible.

Synthesis of Spirotricyclic Core of Bonnadiene

We herein describe a new approach for the efficient synthesis of the tricyclic core of diterpene bonnadiene. The synthetically challenging and unusual [6-7-5] spirotricyclic skeleton including the all-carbon quaternary stereocenter, was installed diastereoselectively via a type II [5 + 2] cycloaddition, followed by a unique vinylogous semipinacol rearrangement. The described chemistry demonstrates the feasibility of making the [6-7-5] spirotricyclic skeleton of the final product from the strained bridged [7-8-5] ring system.

DFT Study of Mechanism and Stereochemistry of Nickel-Catalyzed trans-Arylative Desymmetrizing Cyclization of Alkyne-Tethered Malononitriles

Present here is a density functional theory (DFT) study of the mechanism and origin of enantioselectivity of Ni-catalyzed desymmetric cyclization of alkyne-tethered malononitriles and aryl boronic acids. The reaction starts from transmetalation and arylnickel addition, followed by trans to cis isomerization to give cis-alkenyl nickel species. The stereodetermining step is the CN insertion, which prefers a transition state with the bystander CN group staying away from the ligand to reduce steric repulsion, and gives the final (R)-product.

Total Synthesis of Yuzurine-type Alkaloid Daphgraciline

The first total synthesis of daphgraciline has been achieved, which also represents the first example of the synthesis of Daphniphyllum yuzurine-type alkaloids (∼50 members). The unique bridged azabicyclo[4.3.1] ring system in the yuzurine-type subfamily was efficiently and diastereoselectively assembled via a mild type II [5+2] cycloaddition for the first time. The compact tetracyclic [6-7-5-5] skeleton was installed efficiently via an intramolecular Diels-Alder reaction, followed by a benzilic acid-type rearrangement. The synthetically challenging spiro tetrahydropyran moiety in the final product was installed diastereoselectively via a Ti^III-mediated reductive epoxide coupling reaction. Potential access to enantioenriched daphgraciline is presented.

Ring contraction in synthesis of functionalized carbocycles

Carbocycles are a key and widely present structural motif in organic compounds. The construction of structurally intriguing carbocycles, such as highly-strained fused rings, spirocycles or highly-functionalized carbocycles with congested stereocenters, remains challenging in organic chemistry. Cyclopropanes, cyclobutanes and cyclopentanes within such carbocycles can be synthesized through ring contraction. These ring contractions involve re-arrangement of and/or small molecule extrusion from a parental ring, which is either a carbocycle or a heterocycle of larger size. This review provides an overview of synthetic methods for ring contractions to form cyclopropanes, cyclobutanes and cyclopentanes en route to structurally intriguing carbocycles.

N-Heterocyclic Carbene-Catalyzed [3 + 2] Annulation of 3,3'-Bisoxindoles with α-Bromoenals: Enantioselective Construction of Contiguous Quaternary Stereocenters

An NHC-catalyzed enantio- and diastereoselective [3 + 2] annulation of α-bromoenals with bisoxindoles is developed, affording efficient access to various spirocyclic bisoxindole alkaloids. This protocol tolerates a broad substrates scope, with various spirocyclic bisoxindoles obtained in generally excellent enantioselectivities. More importantly, two contiguous sterically congested all-carbon quaternary stereocenters are successfully created during this process.

Fe-Catalyzed Selective Formal Insertion of Diazo Compounds into C(sp)-C(sp3) Bonds of Propargyl Alcohols: Access to Alkyne-Substituted All-Carbon Quaternary Centers

The construction of all-carbon quaternary centers, especially those containing an alkyne-substituted framework, represents an important challenge in organic synthesis. Here we present a novel Fe-catalyzed selective formal insertion of diazo compounds into C(sp)-C(sp³) bonds of propargyl alcohols under mild conditions that enables the streamlined construction of alkyne-substituted all-carbon quaternary centers. This unique strategy starts with in situ generation of an ester group in the presence of carboxylic acids, followed by insertion of metal-carbene into C(sp)-C(sp³) bonds, which may open up a new reaction mode for exploring metal-carbene insertion into acyclic C-C bonds.

Asymmetric α-Regioselective [3 + 2] Annulation of Morita-Baylis-Hillman Carbonates: Construction of Three Contiguous Stereocenters with Vicinal Quaternary Carbon Centers

Asymmetric α-regioselective annulation of MBH carbonates with 4-arylmethylisoxazol-5-ones has been developed to afford spirocyclic oxindole derivatives containing three contiguous stereogenic centers and vicinal all-carbon quaternary chiral centers. This reaction exhibits a broad substrate scope and excellent functional group tolerance. Excellent yields with high diastereo- and enantioselectivities were obtained in this efficient organocatalytic reaction.

Stereospecific Construction of Quaternary Carbon Stereocenters from Quaternary Carbon Stereocenters

Organoaluminum species promote a smooth nucleophilic substitution at the quaternary carbon stereocenter of stereodefined polysubstituted cyclopropyl methyl phosphate with a complete inversion of configuration, even when more reactive functional groups are present. The regio- and diastereoselectivity of the substitution is attributed to the existence of a bicyclobutonium intermediate.

A Three-Step Process to Facilitate the Enantioselective Assembly of Cis-Fused Octahydrophenanthrenes with a Quaternary Stereocenter

A three-step process for the enantioselective assembly of cis-fused octahydrophenanthrenes with a quaternary stereocenter is reported. This synthetic strategy relies on a regioselective γ-alkylation, a one-pot sequence of asymmetric hydrogenation and oxidation, and an intramolecular enolate arylation to facilitate the rapid and enantioselective construction of cis-fused octahydrophenanthrene scaffolds with an arylated all-carbon quaternary stereocenter concisely and efficiently.

Synergistic Brønsted/Lewis acid catalyzed aromatic alkylation with unactivated tertiary alcohols or di-tert-butylperoxide to synthesize quaternary carbon centers

Dual Brønsted/Lewis acid catalysis involving environmentally benign, readily accessible protic acid and iron promotes site-selective tert-butylation of electron-rich arenes using di-tert-butylperoxide. This transformation inspired the development of a synergistic Brønsted/Lewis acid catalyzed aromatic alkylation that fills a gap in the Friedel-Crafts reaction literature by employing unactivated tertiary alcohols as alkylating agents, leading to new quaternary carbon centers. Corroborated by DFT calculations, the Lewis acid serves a role in enhancing the acidity of the Brønsted acid. The use of non-allylic, non-benzylic, and non-propargylic tertiary alcohols represents an underexplored area in Friedel-Crafts reactivity.

Concise total syntheses of bis(cyclotryptamine) alkaloids via thio-urea catalyzed one-pot sequential Michael addition

Naturally occurring bis(cyclotryptamine) alkaloids feature vicinal all-carbon quaternary stereocenters with an elongated labile C-3a-C-3a' Sigma bond with impressive biological activities. In this report, we have developed a thio-urea catalyzed one-pot sequential Michael addition of bis-oxindole onto selenone to access enantioenriched dimeric 2-oxindoles with vicinal quaternary stereogenic centers at the pseudobenzylic position (up to 96% ee and >20 : 1 dr). This strategy has been successfully applied for the total syntheses of either enantiomers of chimonanthine, folicanthine, and calycanthine.

Strategies for total synthesis of bispyrrolidinoindoline alkaloids

Covering up to 2021Complex cyclotryptamine alkaloids with a bispyrrolidino[2,3-b]indoline (BPI) skeleton are an intriguing family of natural products, exhibiting wide systematic occurrences, large structural diversity, and multiple biological activities. Based on their structural characteristics, BPI alkaloids can be classified into chimonanthine-type BPI alkaloids, BPI diketopiperazines, and BPI epipolythiodiketopiperazines. These intricate molecules have captivated great attention soon after their isolation and identification in the 1960s. Due to the structural complexity, the total synthesis of these cyclotryptamine alkaloids is challenging. Nevertheless, remarkable progress has been achieved in the last six decades; in particular, several methods have been successfully established for the construction of vicinal all-carbon quaternary stereocenters. In this review, the structural diversity and chemical synthesis of these BPI alkaloids were summarized. BPI alkaloids are mainly synthesized by the methods of oxidative dimerization, reductive dimerization, and alkylation of bisoxindole. The purpose of this review is to present overall strategies for assembling the BPI skeleton and efforts towards controlling the stereocenters.

A Green Chemistry Approach toward the Stereospecific Synthesis of Densely Functionalized Cyclopropanes via the Solid-State Photodenitrogenation of Crystalline 1-Pyrazolines

The cyclopropane ring features prominently in active pharmaceuticals, and this has spurred the development of synthetic methodologies that effectively incorporate this highly strained motif into such molecules. As such, elegant solutions to prepare densely functionalized cyclopropanes, particularly ones embedded within the core of complex structures, have become increasingly sought-after. Here we report the stereospecific synthesis of a set of cyclopropanes with vicinal quaternary stereocenters via the solvent-free solid-state photodenitrogenation of crystalline 1-pyrazolines. Density functional theory calculations at the M062X/6-31+G(d,p) level of theory were used to determine the origin of regioselectivity for the synthesis of the 1-pyrazolines; favorable in-phase frontier molecular orbital interactions are responsible for the observation of a single pyrazoline regioisomer. It was also shown that the loss of N₂ may take place via a highly selective solid-state thermal reaction. Scalability of the solid-state photoreaction is enabled through aqueous nanocrystalline suspensions, making this method a "greener" alternative to effectively facilitate the construction of cyclopropane-containing molecular scaffolds.

Tandem 1,6-addition/cyclopropanation/rearrangement reaction of vinylogous para-quinone methides with 3-chlorooxindoles: construction of vicinal quaternary carbon centers

A novel tandem 1,6-addition/cyclopropanation/rearrangement reaction of vinylogous para-quinone methides with 3-chlorooxindoles has been developed, providing dispirooxindole–cyclopentane–cyclohexadienones with vicinal quaternary carbon centers.