Copper(I)-Catalyzed Tandem Carboarylation/Cyclization of Alkynyl Phosphonates with Diaryliodonium Salts

Pd(II)-Catalyzed enantioselective C-H olefination toward the synthesis of P-stereogenic phosphinamides

P-Stereogenic phosphorus compounds are important structural elements in chiral ligands or organocatalysts. Herein, we report a Pd(II)-catalyzed enantioselective C-H olefination toward the synthesis of P-stereogenic phosphinamides using cheap commercially available L-pGlu-OH as a chiral ligand. A broad range of P-stereogenic phosphinamides were gained in good yields with high enantioselectivities (33 examples, up to 77% yield, 99% ee) via desymmetrization and kinetic resolution.

Transition-Metal-Free Electrochemical Selenylative Cyclization of Alkynyl Phosphonates

Unprecedented regioselective electrochemical tandem selenation/cyclization of alkynyl phosphonates with diselenide is described here. These obtained selenoether products can be chemo-selectively converted into halogen-functionalized cyclic enol phosphonates under our electrochemical conditions. These protocols provide straightforward access to valuable cyclic enol phosphonate or phosphaisocoumarins under the electrochemical and transition-metal-free conditions. The robustness of these transformations was illustrated by their compatibility with various complex natural products and bioactive molecules. The selenoether and halogen functional groups allow the further diversification of the phosphorus heterocycles thus obtained.

Design, development and applications of copper-catalyzed regioselective (4 + 2) annulations between diaryliodonium salts and alkynes

Diaryliodonium salts have been extensively applied in organic synthesis as aryl cation equivalents. However, in the electrophilic reactions with alkenes or alkynes, only the electrophilic carbon of the diaryliodonium salts was involved while the other part of the aryl ring was not utilized. Herein, a reaction pattern of diaryliodonium was reported as oxa-1,4-dipoles to undergo (4 + 2) cycloaddition reactions with alkynes. Broad spectrum of the two reaction partners could be utilized in this protocol, enabling an operationally simple, high yielding, and regioselective synthetic approach to isocoumarins. Particularly, good to excellent regioselectivities were achieved for the sterically unbiased unsymmetrical diaryl acetylenes, which was challenging for other transition metal-catalyzed processes. The reaction could be scaled up with the ideal 1:1 stoichiometry and the isocoumarin type natural products Oospolactone and Thunberginol A could be obtained in one or three steps through this methodology.

Vinyl cation-mediated intramolecular hydroarylation of alkynes using pyridinium reagents

Once considered to be exotic species of limited synthetic utility, vinyl cations have recently been shown to be highly versatile intermediates in a variety of processes. Here, we report a method for the synthesis of aryl-substituted benzocycloheptenes and -hexenes using the hydrotriflate salt of an electron-poor pyridine as a uniquely efficient proton source for a vinyl cation mediated Friedel-Crafts cyclization. The mild conditions made possible by this reagent allowed a range of simple and functionalized alkynes bearing pendant aryl groups to serve as suitable substrates for this scalable and convenient protocol.

Copper-Catalyzed Chemo-, Regio-, and Stereoselective Multicomponent 1,2,3-Trifunctionalization of Internal Alkynes

Herein, we report the first diaryliodonium salts promoted multicomponent 1,2,3-trifunctionalization of alkynes, where both the acetylenic bond and the adjacent nonactivated propargylic C(sp³)-H bond were functionalized synergistically to generate α-arylated enones with high chemo-, regio-, and stereoselectivity. A broad spectrum of diaryliodonium salts and internal alkynes could be utilized in this protocol, and a diverse collection of highly substituted and stereochemically defined linear and cyclic complex structures could be elaborated from the enone products.

Recent advances in Cu-catalyzed transformations of internal alkynes to alkenes and heterocycles

Numerous metal-catalyzed reactions involving internal alkynes and aimed towards synthetically and pharmacologically important alkenes and heterocycles have appeared in the literature. Among these, Cu-catalyzed reactions have a special place, which has prompted the investigation and development of carbon-carbon and carbon-heteroatom bond-forming reactions. These reactions possess wide scope, and during the paths of these reactions, either stable or in situ intermediates are formed via the addition of Cu as a core catalyst or synergistic catalyst. In this review, we aim to report different contributions relating to Cu-catalyzed reactions of internal alkynes for the synthesis of different valuable alkenes and heterocycles which have appeared in the literature in the last decade. We anticipate that this appraisal will deliver basic insights for the further advancement of Cu-catalyzed reactions in organic chemistry.

Palladium/Xiao-Phos-Catalyzed Kinetic Resolution of sec-Phosphine Oxides by P-Benzylation

P-stereogenic tert- and sec-phosphines have wide applications in asymmetric catalysis, materials, and pharmaceutical chemistry, however, their practical synthesis still constitutes a significant challenge. Herein, a successful kinetic resolution of rac-secondary phosphine oxides via the enantioselective P-benzylation process catalyzed by the palladium/Xiao-Phos was designed. Both tert- and sec-phosphine oxides were delivered in good yield and excellent enantiopurity (selectivity factor up to 226.1). The appealing synthetic utilities are further demonstrated by the facile preparation of several valuable P-chiral compounds, precursors of bidentate ligands, as well as transition metal complexes.

Concise Synthesis of Phospholene and Its P-Stereogenic Derivatives

A simple method to build phospholene derivatives has been achieved in a one-pot reaction with readily available o-alkynylaryl bromides and alkylphosphine oxides. This method is also applicable to synthesize P-stereogenic phospholenes, and the resulting chiral phosphine was utilized as a ligand for coordination chemistry.

Heteroaryliodonium(III) Salts as Highly Reactive Electrophiles

In recent years, the chemistry of heteroaryliodonium(III) salts has undergone significant developments. Heteroaryliodonium(III) salts have been found to be useful synthetic tools for the transfer of heteroaryl groups under metal-catalyzed and metal-free conditions for the preparation of functionalized heteroarene-containing compounds. Synthetic transformations mediated by these heteroaryliodonium(III) salts are classified into two categories: (1) reactions utilizing the high reactivity of the hypervalent iodine(III) species, and (2) reactions based on unique and new reactivities not observed in other types of conventional diaryliodonium salts. The latter feature is of particular interest and so has been intensively investigated in recent decades. This mini-review therefore aims to summarize the recent synthetic applications of heteroaryliodonium(III) salts as highly reactive electrophiles.

Synthesis of Spirocyclic Compounds by a Ring-Expansion/Cationic Cyclization Cascade Reaction of Chlorosulfate Derivatives

A novel cascade reaction to prepare spirocarbocyclic compounds from chlorosulfate derivatives has been developed. The process involves an unusual thermal elimination of the chlorosulfate moiety, a ring-expansion reaction, and a subsequent cationic cyclization reaction. Despite the relatively complex skeletal rearrangement, the reaction described here is featured by its operational simplicity, being just a thermal process that does not require additional reagents, catalysts, or additives.

Copper-catalyzed O-alkenylation of phosphonates

Copper catalysis allows the direct oxygen alkenylation of dialkyl phosphonates with alkenyl(aryl)iodonium salts with selective transfer of the alkenyl group. This novel methodology proceeds with a wide range of phosphonates under mild conditions and gives straightforward access to valuable enol phosphonates in very good yields.

Access to P-chiral phosphine oxides by enantioselective allylic alkylation of bisphenols

A biscinchona alkaloid-catalyzed AAA reaction for the construction of P-stereogenic center compounds was developed.

A novel biscinchona alkaloid-catalyzed highly enantioselective desymmetrization reaction of bisphenol compounds with achiral Morita–Baylis–Hillman carbonate agents was developed. Through the asymmetric allylic alkylation strategy, a broad range of optically active P-stereogenic phosphine oxides were generated with excellent to good yields (up to 99%) and high enantioselectivities (up to 98.5 : 1.5 e.r.). The reaction was further investigated by the linear free energy relationship (LFER) analysis. A possible transition state was proposed and furthered verified by theoretical calculations.

Transition metal-free access to 3,4-dihydro-1,2-oxaphosphinine-2-oxides from phosphonochloridates and chalcones through tandem Michael addition and nucleophilic substitution

3,4-Dihydro-1,2-oxaphosphinine 2-oxides are synthesized through tandem intermolecular nucleophilic addition and cyclization of phosphonochloridates and enones in the presence of base.