Vinylogous Reaction Research Articles

Unified Enantioselective Allylations and Vinylogous Reactions Enabled by Visible Light-Driven Chiral Lewis Acid Catalysis

Unified Enantioselective Allylations and Vinylogous Reactions Enabled by Visible Light-Driven Chiral Lewis Acid Catalysis

DBU‐Catalyzed Vinylogous Reaction of 3‐Cyano‐4‐methylcoumarins with 3‐Arylsulfonyl‐3‐indolyloxindoles

AbstractAn efficient metal‐free DBU catalyzed approach for the construction of biologically significant quaternary carbon centered C‐3 functionalized 2‐oxindole derivatives through vinylogous reaction of 3‐cyano‐4‐methylcoumarins with 3‐arylsulfonyl‐3‐indolyloxindoles has been developed for first time. The developed protocol is simple, cost‐effective, and producing the desired products in good yields, without utilizing potentially harmful chemicals. Moreover, the synthesized 3,3‐disubstituted 2‐oxindole molecules contain established pharmacophors in their structure, i. e., oxindole‐, indole‐ and coumarin‐ moieties, which makes them a valuable candidate for drug development process.

Enantioselective vinylogous aldol reaction between β,γ-unsaturated amides and isatins

A highly enantioselective vinylogous aldol reaction between β,γ-unsaturated amides and isatins has been developed to provide chiral multifunctional 3-hydroxy-2-oxindoles.

Progress in catalytic asymmetric α-functionalization of vinylogous nucleophilic species

This review summarizes a view of the advances in the catalytic asymmetric α-functionalization of vinylogous nucleophilic species, the content of which is categorized based on the type of vinylogous donor.

Site-Selective, Photocatalytic Vinylogous Amidation of Enones.

Despite the broad interest in organic compounds possessing a γ-aminocarbonyl motif, limited strategies for their synthesis have been reported. Herein, we describe a mild and efficient method for the site-selective amidation of unsaturated enones with electrophilic N-centered radicals as a key intermediate. The photocatalytic vinylogous reaction of dienolates with N-amino pyridinium salts affords γ-amido carbonyl compounds. This process is high-yielding, scalable, and tolerates a broad range of unsaturated α,β-unsaturated carbonyls, including biologically relevant compounds, as starting materials.

A vinylogous Norrish reaction as a strategy for light-mediated ring expansion

Photo-mediated ring expansion using UV-A light. 22 examples, 75–96% yield. The mechanism was investigated by DFT and Transient Absorption Spectroscopy.

Alkynedicobalt mediated vinylogous Nazarov reactions.

The SnCl4 mediated reactions of cross conjugated aryl enynone-Co2(CO)6 and dienynone-Co2(CO)6 complexes afford benzocycloheptynone complexes or cycloheptenynone complexes in a thermal vinylogous Nazarov process. The rate of ring closure is strongly dependent on the ketone α-substituent.

A switch to vinylogous reactivity of vinyl diazo esters for the C-H allylation of benzamides by merging cobalt and photoredox catalysis.

Herein, a de novo vinylogous reactivity of vinyl diazo esters in the C-H bond allylation of benzamides has been developed by coalescing cobalt and photoredox catalysis via C-H activation/allyl carbene migratory insertion. A close relationship between the high valent cobalt catalyst and the photocatalyst has been found to be crucial for this reactivity. The reaction uses oxygen as the sole oxidant and produces benign nitrogen as the only by-product. The reaction shows a good substrate scope with respect to both vinyl diazo esters and benzamides. The utility of the protocol is demonstrated through the late-stage functionalization of several bioactive molecules.

Regiospecific and Enantioselective Arylvinylcarbene Insertion of a C-H Bond of Aniline Derivatives Enabled by a Rh(I)-Diene Catalyst.

Asymmetric insertion of an arylvinylcarbenoid into the C-H bond for direct enantioselective C(sp2)-H functionalization of aniline derivatives catalyzed by a rhodium(I)-diene complex was developed for the first time. The reaction occurred exclusively at the uncommon vinyl terminus site with excellent E selectivity and enantioselectivities, providing various chiral γ,γ-gem-diarylsubstituted α,β-unsaturated esters with broad functional group compatibility under simple and mild conditions. It provides a rare example of the asymmetric C-H insertion of arenes with selective vinylogous reactivity. Synthesis applications of this protocol were featured by several versatile product transformations. Systematic DFT calculations were also performed to elucidate the reaction mechanism and origin of the uncommon enantio- and regioselectivity of the Rh(I)-catalyzed C(sp2)-H functionalization reaction. The measured and computed inverse deuterium kinetic isotope effect supports the C-C bond-formation step as the rate-determining step. Attractive interactions between the chiral ligand and substrates were also proposed to control the enantioselectivity.

Copper(I)-Catalyzed Asymmetric Vinylogous Aldol-Type Reaction of Allylazaarenes.

A vinylogous aldol-type reaction of allylazaarenes and aldehydes is disclosed that affords a series of chiral γ-hydroxyl-α,β-unsaturated azaarenes in moderate to excellent yields with high to excellent regio- and enantioselectivities. With (R,RP )-TANIAPHOS and (R,R)-QUINOXP* as the ligand, the carbon-carbon double bond in the products is generated in (E)-form. With (R)-DTBM-SEGPHOS as the ligand, (Z)-form carbon-carbon double bond is formed in the major product. In this vinylogous reaction, aromatic, α,β-unsaturated, and aliphatic aldehydes are competent substrates. Moreover, a variety of azaarenes, such as pyrimidine, pyridine, pyrazine, quinoline, quinoxaline, quinazoline, and benzo[d]imidazole are well-tolerated. At last, the chiral vinylogous product is demonstrated as a suitable Michael acceptor towards CuI-catalyzed nucleophilic addition with organomagnesium reagents.

Copper(I)‐Catalyzed Asymmetric Vinylogous Aldol‐Type Reaction of Allylazaarenes

AbstractA vinylogous aldol‐type reaction of allylazaarenes and aldehydes is disclosed that affords a series of chiral γ‐hydroxyl‐α,β‐unsaturated azaarenes in moderate to excellent yields with high to excellent regio‐ and enantioselectivities. With (R,RP)‐TANIAPHOS and (R,R)‐QUINOXP* as the ligand, the carbon‐carbon double bond in the products is generated in (E)‐form. With (R)‐DTBM‐SEGPHOS as the ligand, (Z)‐form carbon‐carbon double bond is formed in the major product. In this vinylogous reaction, aromatic, α,β‐unsaturated, and aliphatic aldehydes are competent substrates. Moreover, a variety of azaarenes, such as pyrimidine, pyridine, pyrazine, quinoline, quinoxaline, quinazoline, and benzo[d]imidazole are well‐tolerated. At last, the chiral vinylogous product is demonstrated as a suitable Michael acceptor towards CuI‐catalyzed nucleophilic addition with organomagnesium reagents.

Vinylogous hydrazone strategy for the organocatalytic alkylation of heteroaromatic derivatives.

A new umpolung approach for the asymmetric Friedel-Crafts-type alkylation of electron-poor heteroaromatic systems has been developed. It is based on the vinylogous reactivity of hydrazones derived from heteroaromatic aldehydes. The donating effect of the hydrazone moiety can be efficiently transferred over the heteroaromatic system activating it towards an asymmetric Friedel-Crafts reaction with α,β-unsaturated aldehydes realized under aminocatalytic conditions. Excellent enantioselectivities have been obtained owing to the application of a MacMillan imidazolidinone catalyst. Unmasking of the hydrazone moiety has also been realized resulting in the development of a unique strategy for the asymmetric functionalization of electron-poor heteroaromatic systems.

Asymmetric Construction of Cyclobutanes via Direct Vinylogous Michael Addition/Cyclization of β,γ-Unsaturated Amides.

The construction of cyclobutanes has attracted much attention because of its unique four-membered ring skeleton. Herein, we report the highly enantioselective direct vinylogous Michael reaction of β,γ-unsaturated pyrazole amides and nitroolefin using a squaramide catalyst. Cyclobutane derivatives were obtained by subsequent cyclization in good yields (up to 85%) with excellent enantioselectivities (up to 99% ee). Importantly, the large-scale reaction experiment confirmed the reliability of the vinylogous reaction. Furthermore, the synthetic utility of the vinylogous adducts and cyclobutane derivatives has been realized.

Catalyst-Controlled Selective Alkylation/Cyclopropanation of Indoles with Vinyl Diazoesters.

A catalyst-controlled selective functionalization of indoles with vinyl diazoacetates has been developed. The use of gold catalysts exclusively leads to C3-alkylation products, whereas the highly diastereoselective cyclopropanation reaction is dominant for silver catalysis. Importantly, the gold and silver vinylcarbenes exhibit highly carbenic rather than vinylogous reactivity in these transformations.

Vinylogous Reactivity of Cyclic 2-Enones: Organocatalysed Asymmetric Addition to 2-Enals to Synthesize Fused Carbocycles.

A method for asymmetric and site selective annulations at the γ and γ' positions of cyclic 2-enones with α,β-unsaturated aldehydes has been developed. The organocatalysed [3+3]-annulations proceed with high levels of regio-, diastereo-, and enantioselectivity, affording a series of high value fused carbocycles. Further elaboration gave key lactones (both bridged and fused).

Vinylogous Reactivity of Cyclic 2‐Enones: Organocatalysed Asymmetric Addition to 2‐Enals to Synthesize Fused Carbocycles

AbstractA method for asymmetric and site selective annulations at the γ and γ′ positions of cyclic 2‐enones with α,β‐unsaturated aldehydes has been developed. The organocatalysed [3+3]‐annulations proceed with high levels of regio‐, diastereo‐, and enantioselectivity, affording a series of high value fused carbocycles. Further elaboration gave key lactones (both bridged and fused).

Selective Vinylogous Reactivity of Carbene Intermediate in Gold-Catalyzed Alkyne Carbocyclization: Synthesis of Indenols

A gold-catalyzed carbocyclization of alkynes with a pendant diazo group that is completed by reaction with a protic nucleophile for the synthesis of indenol derivatives with a tertiary center is de...

Enantioselective Synthesis of Trifluoromethyl α,β-Unsaturated δ-Lactones via Vinylogous Aldol-Lactonization Cascade.

The novel vinylogous aldol-lactonization cascade of alkylidene oxindole with trifluoromethyl ketones is presented. The reaction, catalyzed by a bifunctional tertiary amine, provides an efficient application of the vinylogous reactivity of alkylidene oxindoles for the preparation of enantioenriched trifluoromethylated α,β-unsaturated δ-lactones.

A General Asymmetric Formal Synthesis of Aza-Baylis-Hillman Type Products under Bifunctional Catalysis.

A new organocatalytic strategy for the synthesis of enantioenriched aza-Baylis-Hillman type products via a frustrated vinylogous reaction is presented. This process proceeds under mild conditions with good yields, completed Z/E selectivity and excellent enantioselectivities. Moreover, easy derivatizations of the final products led to important building blocks of organic synthesis such as 1,3-aminoalcohols and Lewis base catalysts.

Exploring the Remote Reactivity of π-Extended Carbonyl Compounds: The Vinylogous Alkylidene Malononitrile Activation Strategy

The installation of malononitrile into π-extended carbonyl compounds gives rise to vinylogous alkylidene malononitriles (also known as π-extended dicyanovinylidenes), the direct functionalization of which at remote C(sp3) pronucleophilic sites becomes possible and viable. Starting from easily accessible representative polyunsaturated malononitriles, mild conditions were found to directly couple them to complementary enal acceptors. In all cases, the malononitrile handle proved an indispensable (and optionally traceless) activating ingredient for the vinylogous reactions to proceed efficiently and selectively. Merging the vinylogy concept with the malononitrile HOMO-raising activation strategy and complementary organocatalytic activation modalities (i.e. LUMO-lowering iminium ion activation) turned out to be a successful option, as demonstrated by the number of diverse carbocyclic and heterocyclic chiral products that were (stereo)selectively accessed through this chemistry.1 Introduction2 Reactions of Cyclohexenylidene Malononitriles with Enals3 Reactions of Allylidene Malononitriles with Enals4 Reactions of Indolylmethylene Malononitriles with Enals5 Conclusion