Late-Stage Aryl C-H Bond Cyclopropenylation with Cyclopropenium Cations.

Herein, we disclose the first regio-, site- and chemoselective late-stage (hetero)aryl C-H bond cyclopropenylation with cyclopropenium cations (CPCs). The process is fast, operationally simple and shows an excellent functional group tolerance in densely-functionalized drug molecules, natural products, agrochemicals and fluorescent dyes. Moreover, we discovered that the installation of the cyclopropene ring in drug molecules could not only be used to shield against metabolic instability but also as a synthetic tool to reach medicinally-relevant sp3 -rich scaffolds exploiting the highly-strained nature of the cyclopropene ring with known transformations.

Catalytic Synthesis of Cyclopropenium Cations with Rh-Carbynoids.

Herein, we report the first catalytic one-step synthesis of cyclopropenium cations (CPCs) with readily available alkynes and hypervalent iodine reagents as carbyne sources. Key to the process is the catalytic generation of a novel Rh-carbynoid that formally transfers monovalent cationic carbynes (:+C-R) to alkynes via an oxidative [2+1] cycloaddition. Our process is able to synthesize a new type of CPC substituted with an ester group that underpins the regioselective attack of a broad range of carbon and heteroatomic nucleophiles, thus providing a new platform for the synthesis of valuable cyclopropenes difficult or not possible to make by current methodologies.

Iridium-Catalyzed Asymmetric Allylic Substitution Reactions.

In this review, we summarize the origin and advancements of iridium-catalyzed asymmetric allylic substitution reactions during the past two decades. Since the first report in 1997, Ir-catalyzed asymmetric allylic substitution reactions have attracted intense attention due to their exceptionally high regio- and enantioselectivities. Ir-catalyzed asymmetric allylic substitution reactions have been significantly developed in recent years in many respects, including ligand development, mechanistic understanding, substrate scope, and application in the synthesis of complex functional molecules. In this review, an explicit outline of ligands, mechanism, scope of nucleophiles, and applications is presented.

Regio- and Enantioselective Rhodium-Catalyzed Allylic Alkylation of Racemic Allylic Alcohols with 1,3-Diketones.

Highly regio- and enantioselective rhodium-catalyzed allylic alkylation of 1,3-diketones with racemic secondary allylic alcohols is reported. In the presence of a Rh-catalyst derived from the Carreira (P, olefin)-ligand and TFA as an additive, chiral branched α-allylated 1,3-diketones could be obtained in good to excellent yields, with excellent regio- and enantioselectivity ( b/ l > 19/1, 86-98% ee). The direct utilization of allyl alcohols as electrophiles represents an improvement from the viewpoint of an atom economy. Both aryl- and aliphatic-substituted allyl alcohols are suitable substrates with excellent reaction outcomes. This reaction features mild conditions, broad substrate scope, and readily available substrates.

Rh-Catalyzed aminative dearomatization of 2-naphthols.

A direct aminative dearomatization of 2-naphthols was achieved. In the presence of 1 mol% Rh2(esp)2 and 3 equivalents of O-(2,4-dinitrophenyl)hydroxylamine (DPH) as readily available aminating reagents, the reactions of 2-naphthols afforded unprotected α-amino-ß-naphthalenones in good yields under mild reaction conditions. The conditions were compatible with gram-scale reaction, and the product could undergo diverse transformations.

Iridium-Catalyzed Intermolecular Asymmetric Dearomatization of ß-Naphthols with Allyl Alcohols or Allyl Ethers.

An Ir-catalyzed intermolecular asymmetric dearomatization reaction of ß-naphthols with allyl alcohols or allyl ethers was developed. When an iridium catalyst generated from [Ir(COD)Cl]2 (COD=cyclooctadiene) and a chiral P/olefin ligand is employed, highly functionalized ß-naphthalenone compounds bearing an all-carbon-substituted quaternary chiral center were obtained in up to 92 % yield and 98 % ee. The direct utilization of allyl alcohols as electrophiles represents an improvement from the viewpoint of atom economy. Allyl ethers were found to undergo asymmetric allylic substitution reaction under Ir catalysis for the first time. The diverse transformations of the dearomatized product to various motifs render this method attractive.

Palladium(0)-Catalyzed Intermolecular Arylative Dearomatization of ß-Naphthols.

The first Pd0 -catalyzed intermolecular arylative dearomatization of ß-naphthols with aryl halides is described. It was found that Q-Phos could facilitate the palladium-catalyzed cross-coupling-type dearomatization of ß-naphthols, while avoiding O-arylation, to construct 2-naphthalenones in excellent yields and with high chemoselectivity.

Time-dependent enantiodivergent synthesis via sequential kinetic resolution.

The preparation of both enantiomers of chiral molecules is among the most fundamental tasks in organic synthesis, medicinal chemistry and materials science. Achieving this goal typically requires reversing the absolute configuration of the chiral component employed in the reaction system that is being used. The task becomes challenging when the natural source of the chiral component is not available in both configurations. Herein, we report a time-dependent enantiodivergent synthesis, in which an Ir-catalysed allylic substitution reaction uses one catalyst sequentially to promote two kinetic resolution reactions, enabling the synthesis of both enantiomers of the product using the same enantiomer of a chiral catalyst. The appropriate permutation of individual reaction rates is essential for the isolation of the chiral products in opposite configurations with high enantiopurity when quenched at different reaction times. This work provides an alternative solution for the preparation of both enantiomers of chiral molecules.

Rhodium-Catalyzed Asymmetric Allylic Dearomatization of ß-Naphthols: Enantioselective Control of Prochiral Nucleophiles.

A highly enantioselective rhodium-catalyzed allylic dearomatization of ß-naphthols with racemic aryl vinyl carbinol is described. In the presence of a Rh-catalyst derived from [Rh(C2H4)Cl]2 and chiral (P, olefin)-ligand with TFA as an additive, the functionalized ß-naphthalenone compounds bearing an all-carbon-substituted quaternary stereogenic center were obtained in good yields with excellent enantioselectivity. In addition, this protocol features the enantioselective control of prochiral nucleophiles and provides the first illustration of Rh-catalyzed asymmetric allylic dearomatization.

Ligand-enabled Ir-catalyzed intermolecular diastereoselective and enantioselective allylic alkylation of 3-substituted indoles.

An Ir-catalyzed asymmetric allylic alkylation of 3-substituted indoles is reported. The reaction provides indoline products containing multiple contiguous stereocenters with high site-, regio-, diastereo- and enantioselectivities in one step from a wide range of readily available starting materials. The key to this method is the high level of diastereocontrol enabled by an iridium catalyst derived from a N-aryl phosphoramidite ligand (Me-THQphos, 1c).