Phosphine-Catalyzed Aza-MBH Reactions of Vinylpyridines: Efficient and Rapid Access to 2,3,5-Triarylsubstituted 3-Pyrrolines

One-pot catalyst-free synthesis of benzopyrroxazine derivatives by a mutually activated sequential annulation process

A one-pot catalyst-free reaction of o-hydroxyaryl azomethine ylides, vinyl pyridines and paraformaldehyde for the synthesis of benzopyrroxazines is reported, which offers a straightforward and atom-economical procedure for the preparation of benzopyrroxazine derivatives in moderate to excellent yields under mild conditions. A self-catalyzed [3 + 2] annulation through a mutual activation method and a sequential non-catalyzed [5 + 1] annulation process contribute to this strategy. The corresponding control experiments have been conducted to reveal the mechanism of this reaction.

[4 + 2] Cycloaddition of trifluoromethyl ketimines with 2-alkenyl azaarenes through selective C–F bond cleavage of CF3

A transition-metal-free [4 + 2] cycloaddition of trifluoromethyl ketimines with 2-alkenyl azaarenes through selective C–F bond cleavage of CF₃ has been developed to afford cis-tetrahydroxypyridine products in moderate yields under mild conditions.

Transition-metal-free decarbonylative alkylation towards N-aryl α-hydroxy amides via triple C–C bond cleavages and their selective deuteration

A transition-metal-free decarbonylative alkylation reaction for the synthesis of N-aryl α-hydroxy amides via precise cleavages and reorganizations of three C–C σ bonds has been developed.

Enantioselective [4 + 2] Cycloaddition Reaction of Vinylquinolines with Dienals Enabled by Synergistic Organocatalysis

An unprecedented organocatalytic enantioselective [4 + 2] cycloaddition reaction of vinyl quinolines with dienals is achieved with the synergistic activation of CH₃SO₃H and a chiral aminocatalyst. The power of the process is demonstrated by its high efficiency of the production of new synthetically and biologically valued chiral quinoline architectures in high yields and with excellent enantioselectivities.

Sulfur-directed palladium-catalyzed C(sp3)–H α-arylation of 3-pyrrolines: easy access to diverse polysubstituted pyrrolidines

A sulfur-directed palladium-catalyzed C(sp³)–H α-arylation of 3-pyrrolines with arylboronic acids has been disclosed, providing a range of 2-aryl-3-pyrolines, which could be readily converted to various polysubstituted pyrrolidines.

Construction of N-Alkyl- and N-Arylaziridines from Unprotected Amines via C-H Oxidative Amination Strategy

A copper-promoted intramolecular C-H oxidative amination reaction between secondary amine (N-H) and C(sp³)-H at the benzylic position of azaarenes or α-position of ketones for the synthesis of aziridine derivatives has been developed. Moreover, a practical annulation of electron-deficient vinylarenes with an unprotected primary alkyl amine by a Yb(OTf)₃-CuI relay system has also been reported. The reactions were carried out with oxygen as the sole oxidant to give the N-alkyl- and N-arylaziridines in good yields.

Phosphine-catalyzed fixation of CO2 with γ-hydroxyl alkynone under ambient temperature and pressure: kinetic resolution and further conversion

Phosphine-catalyzed fixation of CO₂ with γ-hydroxyl alkynone under ambient temperature and pressure was achieved and the first example of chiral phosphine catalyzed kinetic resolution of propargyl alcohols via carbon dioxide fixation was demonstrated.

Vinyl-1,2,4-oxadiazoles Behave as Nucleophilic Partners in Morita-Baylis-Hillman Reactions

We describe that vinyl-oxadiazoles function as a new and efficient nucleophilic partner for the Morita-Baylis-Hillman (MBH) reaction. The reaction between 5-vinyl-3-aryl-1,2,4-oxadiazoles and aromatic and aliphatic aldehydes, catalyzed by DABCO in the absence of solvent, showed high efficiency to afford a new class of heterocyclic MBH adducts with potential biological activity on yields up to 99% and short reaction times. These synthetically attractive adducts bear a heterocyclic scaffold of large pharmaceutical and commercial interest associated with a plethora of biological effects and technological applications. We also demonstrate their synthetic usefulness by a photoinduced addition reaction to a polyfunctionalized amino alcohol.

Highly Efficient and Diastereoselective Construction of Trifluoromethyl-Containing Spiro[pyrrolidin-3,2'-oxindole] by a Catalyst-free Mutually Activated [3+2] Cycloaddition Reaction

A catalyst-free self-catalyzed [3+2] cycloaddition reaction of isatin-derived α-(trifluoromethyl)imines with vinylpyridines is reported. The reaction offers a straightforward and atom-economical procedure for the preparation of a series of 5'-trifluoromethyl-spiro[pyrrolidin-3,2'-oxindoles] in excellent yields and diastereoselectivities. The reaction mechanism has been investigated by control experiments, DFT calculation of pK_a values and the kinetic profiles, revealing that this reaction featured the mutual activation between isatin-derived α-(trifluoromethyl)imines and vinylpyridine to generate the reactive species.

Visible light-promoted umpolung coupling of aryl tri-/difluoroethanones with 2-alkenylpyridines

A metal-free, mild, and simple protocol is developed for the synthesis of tertiary alcohols bearing tri-/difluoromethyl groups upon visible-light irradiation.

Alkenylazaarenes as dipolarophiles in 1,3-dipolar cycloaddition of nitrones: regioselectivity-switchable and highly diastereoselective synthesis of multisubstituted isoxazolidines

Metal free 1,3-dipolar cycloaddition between alkenylazaarenes and nitrones has been developed for the synthesis of 4-substituted isoxazolidines and 5-substituted isoxazolidines in good yields and selectivities.

Co(OAc)2-Catalyzed Trifluoromethylation and C(3)-Selective Arylation of 2-(Propargylamino)pyridines via a 6-Endo-Dig Cyclization

A Co(OAc)₂-catalyzed trifluoromethylation and subsequent C(3)-selective arylation of 2-(propargylamino)pyridines has been developed. A new 6-endo-dig cyclization involving an unprecedented C(3) selective arylation of the pyridines instead of a commonly observed 5-exo-dig cyclization with "N" is realized. Moreover, the study presents the first case of the installation of a trifluoromethyl group into electron-deficient azaarenes. The process delivers an efficient cascade approach to new trifluoromethylated 1,8-naphthyridine structures with a broad substrate scope.

β-Selective Reductive Coupling of Alkenylpyridines with Aldehydes and Imines via Synergistic Lewis Acid/Photoredox Catalysis

Umpolung (polarity reversal) strategies of aldehydes and imines have dramatically expanded the scope of carbonyl and iminyl chemistry by facilitating reactions with non-nucleophilic reagents. Herein, we report the first visible light photoredox-catalyzed β-selective reductive coupling of alkenylpyridines with carbonyl or iminyl derivatives with the aid of a Lewis acid co-catalyst. Our process tolerates complex molecular scaffolds (e.g., sugar, natural product, and peptide derivatives) and is applicable to the preparation of compounds containing a broad range of heterocyclic moieties. Mechanistic investigations indicate that the key step involves single-electron-transfer reduction of aldehydes or imines followed by the addition of resulting ketyl or α-aminoalkyl radicals to Lewis acid-activated alkenylpyridines.

Transition-metal-free synthesis of indolizines via [3 + 2]-annulation from α-bromoenals and 2-substituted azaarenes

A transition-metal-free “one-pot” synthetic approach for the synthesis of indolizines from α-bromo-substituted enals and simple 2-substituted azaarenes has been developed.

Tunable regiodivergent phosphine-catalyzed [3 + 2] cycloaddition of alkynones and trifluoroacetyl phenylamides

The regiodivergent phosphine-catalyzed [3 + 2] cycloaddition of 2-(2,2,2-trifluoroacetyl)phenylamides and alkynones have been achieved through adjusting the acidities of substrates, changing reaction temperature and addition of protic additive H₂O. The detailed mechanism was systematically studied.

Construction of an all-carbon quaternary stereocenter by organocatalytic enantioselective α-functionalization of α-substituted β-ketocarbonyls with electron deficient vinylarenes

An all-carbon quaternary stereocenter is efficiently constructed by a chiral amine catalyzed enantioselective α-functionalization of α-substituted β-ketocarbonyls with electro-deficient vinylarenes.