Yuya Hu

An atom economical palladium‐catalyzed addition reaction has been developed to stereoselectively access tetrasubstituted alkenyl iodides. A palladium catalyst bearing 1,2‐bis[bis(pentafluorophenyl)phosphino]ethane (dAr^Fpe), an electron‐poor bidentate ligand, is essential to promote the high yielding and chemoselective reaction between alkynes and aryl iodides.

Abstract

A completely atom economical palladium‐catalyzed addition reaction has been developed to stereoselectively access functionalized tetrasubstituted alkenyl iodides. The palladium catalyst, which bears an electron‐poor bidentate ligand rarely employed in catalysis, is essential to promote the high yielding and chemoselective intermolecular reaction between equimolar amounts of an alkyne and an aryl iodide. This new carbohalogenation reaction is an attractive alternative to traditional synthetic methods, which rely on multistep synthetic sequences and protecting‐group manipulations.

The activation and functionalization of C‐F bonds has garnered significant attention in the scientific community as a strategy to mitigate toxicity and environmental concerns, as well as provide new pathways to agro‐ and pharmaceutical chemicals and materials. While several transition metal systems have been developed for this transformation, the use of main group compounds remains less explored. In recent years, several strategies to C‐F bond activation have focused on the use of phosphorus‐based reagents. In this review, we provide an overview of strategies that exploit P(V) and P(III)‐based Lewis acids as well as P(III) Lewis bases in frustrated Lewis pair (FLP)‐protocols for hydrodefluorination, C‐C couplings and C‐F derivatizations.

A procedure for the synthesis of N‐methyl‐arylamines directly from nitroarenes using methanol as green methylating agent was developed. Key to success is the use of a specific catalyst system consisting of palladium acetate and the ligand 1‐​[2,​6‐​bis(isopropyl)​phenyl]​‐​2‐​[tert‐butyl(2‐pyridinyl)phosphi​no]​‐1H‐​Imidazole (L1). The generality of this protocol is demonstrated in the synthesis of more than 20 N‐methyl‐arylamines under comparably mild conditions. Combining this novel methodology with subsequent coupling processes using the same catalyst allows for efficient diversification of aromatic nitro compounds to a broad variety of amines including drug molecules.

Reductive functionalization of CO2 combining both the formation of the new bonds and CO2 reduction in the presence of reductant, e.g. molecular hydrogen, hydrosilane or hydroborane has become increasingly attractive, which enlarges the spectra of compounds directly available from CO2 thus provides fresh idea for CO2 chemistry. This microreview briefly summarizes recent advances in new bond construction using CO2 as formyl, methylene and methyl source with transition‐metal catalyst, which are divided into sections according to C‐N, C‐C and C‐O bonds formation in the presence of nitrogen‐, carbon‐ and oxygen‐nucleophiles respectively. In the end, the challenges and opportunities with future trend of the reductive functionalization of CO2 are also discussed.

Cycloaddition reactions provide direct and convergent routes to cycloalkanes, making them valuable targets for the development of synthetic methods. Whereas six-membered rings are readily accessible from Diels-Alder reactions, cycloadditions that generate five-membered rings are comparatively limited in scope. Here, we report that dinickel complexes catalyze [4 + 1]-cycloaddition reactions of 1,3-dienes. The C₁ partner is a vinylidene equivalent generated from the reductive activation of a 1,1-dichloroalkene in the presence of stoichiometric zinc. Intermolecular and intramolecular variants of the reaction are described, and high levels of asymmetric induction are achieved in the intramolecular cycloadditions using a C₂-symmetric chiral ligand that stabilizes a metal-metal bond.

NHC organocatalysis: A straightforward organocatalytic method for the direct carboxylation of terminal alkynes towards propargylic esters, is reported. A simple, widely‐available, stable, and cost‐efficient N‐heterocyclic carbene precursor salt was used as the (pre)catalyst.

Abstract

An efficient and straightforward organocatalytic method for the direct, multicomponent carboxylation of terminal alkynes with CO₂ and organochlorides, towards propargylic esters, is reported for the first time. 1,3‐Di‐tert‐butyl‐1H‐imidazol‐3‐ium chloride, a simple, widely‐available, stable, and cost‐efficient N‐heterocyclic carbene (NHC) precursor salt was used as the (pre)catalyst. A wide range of phenylacetylenes, bearing electron‐withdrawing or electron‐donating substituents, react with allyl‐chlorides, benzyl chlorides, or 2‐chloroacetates, providing the corresponding propargylic esters in low to excellent yields. DFT calculations on the mechanism of this transformation indicate that the reaction is initiated with the formation of an NHC‐carboxylate, by addition of the carbene to a molecule of CO₂. Then, the nucleophilic addition of this species to the corresponding chlorides has been computed to be the rate limiting step of the process.

The first selective carbonylations of gem‐difluoroalkenes was developed, providing a general approach to a variety of synthetically useful difluoromethylated esters in high yields and excellent regioselectivities.

Abstract

The first catalyst for the alkoxycarbonylation of gem‐difluoroalkenes is described. This novel catalytic transformation proceeds in the presence of Pd(acac)₂/1,2‐bis((di‐tert‐butylphosphan‐yl)methyl)benzene (btbpx) (L4) and allows for an efficient and straightforward access to a range of difluoromethylated esters in high yields and regioselectivities. The synthetic utility of the protocol is showcased in the practical synthesis of a Cyclandelate analogue using this methodology as the key step.