Asymmetric Pauson−Khand-type Reaction Mediated by Rh(I) Catalyst at Ambient Temperature

Cationic Rhodium(I)-Catalyzed Asymmetric Cyclohydroformylation of 1,6-Enynes with Formaldehyde

We report a rhodium(I)-catalyzed asymmetric cyclohydroformylation reaction of 1,6-enynes with formaldehyde. The reaction of 1,6-enynes with formaldehyde in the presence of a cationic Rh(I) catalyst, such as [Rh(cod)₂ ]⁺ OTf^- , and a chiral biaryl diphosphine led to asymmetric cyclohydroformylation to produce aldehydes with higher-order structures highly enantioselectively. This transformation procedure is applicable to a variety of enynes, with wide compatibility in various atoms liking between the alkyne and alkene parts, substituents at the alkyne terminus, and substituents at the alkene part, being converted to newly formed aldehydes in 14% to 90% yields with 50% to 98% ee. The products were further transformed with various nucleophiles to alcohols, an amine, and a diene without loss of chirality at their γ-position.

Rhodium-Catalyzed Enantioselective and Desymmetrizative Pauson-Khand Reaction: Access to Tricyclo[6.2.1.04,11]undecenes

Rhodium-catalyzed asymmetric desymmetrization Pauson-Khand reaction of C4-alkynyl-tethered cyclohexadienones has been developed as a novel strategy for access to fused 6-5-5 tricycles bearing three consecutive stereogenic centers. An array of chiral tricyclo[6.2.1.0^4,11]undecenes have been synthesized in high yields and enantioselectivities in a single step under mild conditions. This strategy employs readily accessible internal-olefin-containing 1,6-enynes, providing a potentially powerful tool for constructing chiral polycyclic scaffolds of complex molecules containing cyclopentenones and cyclohexenones.

Regioselectivity of the Pauson-Khand reaction in single-walled carbon nanotubes

Chemical functionalization of nanotubes, in which their properties can be combined with those of other classes of materials, is fundamental to improve the physicochemical properties of nanotubes for potential technological applications. In this work, we theoretically and experimentally examine the Pauson-Khand reaction (PKR) on zig-zag, armchair, and chiral single-walled carbon nanotubes (SWCNTs). Our benchmarked density functional theory (DFT) calculations show that an alternative pathway to the widely accepted Magnus reaction pathway has significantly lower energy barriers, thus suggesting the use of this alternative pathway to predict whether a PKR on SWCNTs is favored or hampered. Accessible energy barriers of up to 16 kcal mol-1 are estimated and our results suggest that semiconducting SWCNTs react faster than metallic ones, although both types can be functionalized. Guided by our theoretical predictions, cyclopentenones are successfully attached to SWCNTs by heating and are, subsequently, characterized in the laboratory.

Recent advances in rhodium-catalyzed asymmetric synthesis of heterocycles

Heterocycles are crucial structural motifs that are ubiquitously present in biologically active natural products and pharmaceutically important compounds. Over the past few decades, great attention has been paid to develop efficient methodologies for the construction of diverse enantioenriched heterocyclic frameworks. This review focuses on the recent impressive progress and advances in the asymmetric synthesis of heterocycles under rhodium catalysis.

Computationally Guided Catalyst Design in the Type I Dynamic Kinetic Asymmetric Pauson-Khand Reaction of Allenyl Acetates

The Rh(I)-catalyzed allenic Pauson-Khand reaction (APKR) is an efficient, redox-neutral method of synthesizing α-acyloxy cyclopentenones. An enantioselective APKR could provide access to chiral, nonracemic α-acyloxy and α-hydroxy cyclopentenones and their corresponding redox derivatives, such as thapsigargin, a cytotoxic natural product with potent antitumor activity. Rapid scrambling of axial chirality of allenyl acetates in the presence of Rh(I) catalysts enables the conversion of racemic allene to enantiopure cyclopentenone product in a dynamic kinetic asymmetric transformation (DyKAT). A combined experimental and computational approach was taken to develop an effective catalytic system to achieve the asymmetric transformation. The optimization of the denticity, and steric and electronic properties of the ancillary ligand (initially (S)-MonoPhos, 58:42 er), afforded a hemilabile bidentate (S)-MonoPhos-alkene-Rh(I) catalyst that provided α-acyloxy cyclopentenone product in up to 14:86 er. Enantioselectivity of the Rh(I)-(S)-MonoPhos-alkene catalyst was rationalized using ligand-substrate steric interactions and distortion energies in the computed transition states. This asymmetric APKR of allenyl acetates is a rare example of a Type I DyKAT reaction of an allene, the first example of DyKAT in a cyclocarbonylation reaction, and the first catalyst-controlled enantioselective APKR.

Rh(I)-catalyzed intramolecular [2 + 2 + 1] cycloaddition of allenenes: Construction of bicyclo[4.3.0]nonenones with an angular methyl group and tricyclo[6.4.0.0]dodecenone

The [RhCl(CO)dppp]₂-catalyzed intramolecular carbonylative [2 + 2 + 1] cycloaddition of allenenes was developed to prepare bicyclo[4.3.0]nonenones possessing a methyl group at the ring junction, which is difficult to achieve by the Pauson–Khand reaction of the corresponding enynes. This method also provided a new procedure for the construction of the tricyclo[6.4.0.0^1,5]dodecenone framework in a satisfactory yield.