Copper-catalyzed enantioselective diyne cyclization via C(sp2)-O bond cleavage

Copper-Catalyzed Triyne Cyclization via Vinyl Cations

Herein, we describe an efficient copper-catalyzed cyclization of triynes via vinyl cation intermediates. The reaction leads to the practical and atom-economical synthesis of valuable polycyclic pyrroles by constructing three new rings in one step under mild reaction conditions. The proposed reaction mechanism shows the ordered and regioselective reaction of alkynes. Moreover, the possibility of such an asymmetric triyne cyclization also emerges.

Enantioselective Synthesis of Axially Chiral Tetrasubstituted Alkenes by Copper-Catalyzed C(sp2)-H Functionalization of Arenes with Vinyl Cations

Axially chiral tetrasubstituted alkenes are of increasing value and interest in chemistry-related areas. However, their catalytic asymmetric synthesis remains elusive, owing to the high steric repulsion and relatively low conformational stability. Herein, we disclose the straightforward construction of atropisomeric tetrasubstituted alkenes by effective enantiocontrol in a reaction with vinyl cation intermediates. This copper-catalyzed enantioselective C(sp2)-H functionalization of sterically hindered (hetero)arenes with vinyl cations enables the efficient and atom-economical preparation of axially chiral acyclic tetrasubstituted styrenes and pyrrolyl ethylenes with high atroposelectivities. Importantly, this reaction represents the first example of the assembly of axially chiral alkenes via vinyl cations. Computational mechanistic studies reveal the reaction mechanism, origin of regioselectivity, Z/E selectivity and enantioselectivity. The synthetic utility has been demonstrated by diverse product derivatizations, chiral organocatalyst synthesis, as well as further applications in asymmetric catalysis.

Oxidative Cleavage of Aromatic C-O Linkages by Oxoammonium Salts

Oxidative cleavage of aromatic C(sp2)-O bond is important to the conversion of biomass and plastic wastes into value-added chemicals. Here we put forward the oxidative cleavage of para-C-O bonds in phenolic compounds in use of oxoammonium salts as oxidant and water as the oxygen source. The mechanism is that oxoammonium cation activates water to form hydroxy-oxoammonium adduct and thus realizes the ipso-substitution of 4-alkoxyphenol, which is proved by substituent effect, isotope labelling experiments, and kinetic analysis. Furthermore, this protocol is successfully applied into the depolymerization of both lignin model compounds with α-O-5 and 4-O-5 linkages and polyphenylene oxide (PPO).

Copper-Catalyzed Enantioselective Dehydro-Diels-Alder Reaction: Atom-Economical Synthesis of Axially Chiral Carbazoles

The dehydro-Diels-Alder (DDA) reaction is a powerful method for the construction of aromatic compounds. However, the enantioselective DDA reaction has been rarely developed, probably due to the competitive thermal reaction. Herein, we report a copper-catalyzed enantioselective DDA reaction through vinyl cation pathway. The reaction leads to the atom-economical synthesis of axially chiral phenyl and indolyl carbazoles in generally excellent yields with good to excellent atroposelectivities. This methodology represents the first example of non-noble metal-catalyzed enantioselective DDA reaction. Notably, new chiral ligand and organocatalyst derived from the constructed axially chiral carbazole are demonstrated to be useful in asymmetric catalysis.

Asymmetric one-carbon ring expansion of diverse N-heterocycles via copper-catalyzed diyne cyclization

One-carbon ring expansion reaction of N-heterocycles has gained particular attention in the past decade because this method allows for the conversion of readily available N-heterocycles into potentially useful complex ring-expanded N-heterocycles, which are inaccessible by traditional methods. However, the catalytic asymmetric variant of this reaction has been rarely reported to date. Herein, we disclose an enantioselective one-carbon ring expansion reaction through chiral copper-catalyzed diyne cyclization, leading to the practical, atom-economic and divergent assembly of an array of valuable chiral N-heterocycles bearing a quaternary stereocenter in generally good to excellent yields with excellent enantioselectivities (up to >99% ee). This protocol represents the first example of asymmetric one-carbon ring expansion reaction of N-heterocycles based on alkynes.

Catalytic Epoxidation of Carbonyl Compounds via Carbonyl Ylides: from Racemic to Enantioselective

Transition metal-catalyzed epoxidation of carbonyl compounds through carbonyl ylides represents a highly effective method for synthesizing a diverse range of valuable epoxides. This review offers an in-depth overview of the latest developments in inter- and intramolecular epoxidation reactions involving metal carbenes and carbonyl compounds, encompassing both racemic to enantioselective transformations. These catalytic epoxidations are reviewed by highlighting their product selectivity, diversity and applicability, and the related mechanistic rationale is showcased where possible.

Enantioselective functionalization of unactivated C(sp3)-H bonds through copper-catalyzed diyne cyclization by kinetic resolution

Site- and stereoselective C-H functionalization is highly challenging in the synthetic chemistry community. Although the chemistry of vinyl cations has been vigorously studied in C(sp3)-H functionalization reactions, the catalytic enantioselective C(sp3)-H functionalization based on vinyl cations, especially for an unactivated C(sp3)-H bond, has scarcely explored. Here, we report an asymmetric copper-catalyzed tandem diyne cyclization/unactivated C(sp3)-H insertion reaction via a kinetic resolution, affording both chiral polycyclic pyrroles and diynes with generally excellent enantioselectivities and excellent selectivity factors (up to 750). Importantly, this reaction demonstrates a metal-catalyzed enantioselective unactivated C(sp3)-H functionalization via vinyl cation and constitutes a kinetic resolution reaction based on diyne cyclization. Theoretical calculations further support the mechanism of vinyl cation-involved C(sp3)-H insertion reaction and elucidate the origin of enantioselectivity.

Copper-catalyzed atroposelective formal [4+1] annulation of 1,2-diketones with vinyl cations

The enantioselective transformation of easily accessible 1,2-diketones represents a quick pathway towards enantioenriched molecules. Herein, we disclose a copper-catalyzed atroposelective formal [4+1] annulation of 1,2-diketones with vinyl cations, enabling the efficient and atom-economical construction of axially chiral arylpyrroles bearing 1,3-dioxole moieties with good to excellent enantioselectivities under mild reaction conditions. Importantly, this methodology constitutes the first enantioselective formal [4+1] annulation of 1,2-diketones.

Synthesis of a new fluorophore: wavelength-tunable bisbenzo[f]isoindolylidenes

The creation of new functional molecules is a central task in chemical synthesis. Herein, we report the synthesis of a new type of fluorophore, bisbenzo[f]isoindolylidenes, from easily accessible dipropargyl benzenesulfonamides. Wavelength-tunable fluorophores emitting strong fluorescence of green to red light were obtained in this reaction. Late-stage modifications and incorporation of bioactive molecules into these fluorophores give rise to potential applications in biological studies. Detailed computational and experimental studies were conducted to elucidate the mechanism, and suggest a reaction sequence involving Garratt-Braverman type cyclization, isomerization, fragmentation, dimerization and oxidation.

Copper-catalyzed intermolecular formal (5 + 1) annulation of 1,5-diynes with 1,2,5-oxadiazoles

One-carbon homologation reactions based on one-carbon insertion into the N-O bond of heterocycles have received tremendous interest over the past decades. However, these protocols have to rely on the use of hazardous and not easily accessible diazo compounds as precursors, and examples of the relevant asymmetric catalysis have not been reported. Here we show that a copper-catalyzed intermolecular formal (5 + 1) annulation of 1,5-diynes with 1,2,5-oxadiazoles involving one-carbon insertion into the heterocyclic N-O bond via non-diazo approach. This method enables practical and atom-economic synthesis of valuable pyrrole-substituted oxadiazines in generally moderate to good yields under mild reaction conditions. In addition, the possibility of such an asymmetric formal (5 + 1) annulation also emerges.