Rhodium-catalysed intermolecular alkyne hydroacylation: the enantioselective synthesis of α- and β-substituted ketones by kinetic resolution

Rhodium-Catalyzed Asymmetric C-H Functionalization Reactions

This review summarizes the advancements in rhodium-catalyzed asymmetric C-H functionalization reactions during the last two decades. Parallel to the rapidly developed palladium catalysis, rhodium catalysis has attracted extensive attention because of its unique reactivity and selectivity in asymmetric C-H functionalization reactions. In recent years, Rh-catalyzed asymmetric C-H functionalization reactions have been significantly developed in many respects, including catalyst design, reaction development, mechanistic investigation, and application in the synthesis of complex functional molecules. This review presents an explicit outline of catalysts and ligands, mechanism, the scope of coupling reagents, and applications.

Sequential Catalytic Functionalization of Aryltriazenyl Aldehydes for the Synthesis of Complex Benzenes

We demonstrate that aryltriazenes can promote three distinctive types of C–H functionalization reactions, allowing the preparation of complex benzene molecules with diverse substitution patterns. 2-Triazenylbenzaldehydes are shown to be efficient substrates for Rh(I)-catalyzed intermolecular alkyne hydroacylation reactions. The resulting triazene-substituted ketone products can then undergo either a Rh(III)-catalyzed C–H activation, or an electrophilic aromatic substitution reaction, achieving multifunctionalization of the benzene core. Subsequent triazene derivatization provides traceless products.

Rhodium-catalyzed sequential intermolecular hydroacylation and deconjugative isomerization toward diversified diketones

A rhodium(i)-catalyzed reaction via an intermolecular hydroacylation/deconjugative isomerization cascade was developed which enabled the facile synthesis of valuable 1,4-, 1,5-, and 1,6-diketones with good to excellent yields.

Dynamic Kinetic Resolution of Aldehydes by Hydroacylation

We report a dynamic kinetic resolution (DKR) of chiral 4-pentenals by olefin hydroacylation. A primary amine racemizes the aldehyde substrate via enamine formation and hydrolysis. Then, a cationic rhodium catalyst promotes hydroacylation to generate α,γ-disubstituted cyclopentanones with high enantio- and diastereoselectivities.

Tailored trisubstituted chiral Cp x RhIII catalysts for kinetic resolutions of phosphinic amides

A trisubstituted chiral Cp^x ligand family is introduced.

A trisubstituted chiral Cp^x ligand family is introduced. Based on the disubstituted atropchiral Cp^x ligand scaffold, the introduction of a bulky third substituent at the central position of the Cp ring leads to substantially increased selectivities for rhodium(iii)-catalyzed kinetic resolutions and allowed for s-factors of up to 50. Their superiority is demonstrated by kinetic resolutions of phosphinic amides providing access to compounds with stereogenic phosphorus(v) atoms. The unreacted acyclic phosphinic amide and the cyclized product are both obtained in good yields and enantioselectivities. The ligand synthesis capitalizes on a late stage modification and expands the accessible ligand Cp^x ligand portfolio.

Two-Component Assembly of Thiochroman-4-ones and Tetrahydrothiopyran-4-ones Using a Rhodium-Catalyzed Alkyne Hydroacylation/Thio-Conjugate-Addition Sequence

β'-Thio-substituted-enones, assembled from the combination of β-tert-butylthio-substituted aldehydes and alkynes, using rhodium catalysis, are shown to smoothly undergo in situ intramolecular S-conjugate addition to deliver a range of S-heterocycles in a one-pot process. Aryl, alkenyl, and alkyl aldehydes can all be employed, to provide thiochroman-4-ones, hexahydro-4H-thiochromen-4-ones, and tetrahydrothiopyran-4-ones, respectively. A variety of in situ oxidations are also performed, allowing access to S,S-dioxide derivatives, as well as unsaturated variants.

Traceless Rhodium-Catalyzed Hydroacylation Using Alkyl Aldehydes: The Enantioselective Synthesis of β-Aryl Ketones

A one-pot three-step sequence involving Rh-catalyzed alkene hydroacylation, sulfide elimination and Rh-catalyzed aryl boronic acid conjugate addition gave products of traceless chelation-controlled hydroacylation employing alkyl aldehydes. The stereodefined β-aryl ketones were obtained in good yields with excellent control of enantioselectivity. Good variation of all three reaction components is possible.

Direct Synthesis of Highly Substituted Pyrroles and Dihydropyrroles Using Linear Selective Hydroacylation Reactions

Rhodium(I) catalysts incorporating small bite-angle diphosphine ligands, such as (Cy2 P)2 NMe or bis(diphenylphosphino)methane (dppm), are effective at catalysing the union of aldehydes and propargylic amines to deliver the linear hydroacylation adducts in good yields and with high selectivities. In situ treatment of the hydroacylation adducts with p-TSA triggers a dehydrative cyclisation to provide the corresponding pyrroles. The use of allylic amines, in place of the propargylic substrates, delivers functionalised dihydropyrroles. The hydroacylation reactions can also be combined in a cascade process with a Rh(I) -catalysed Suzuki-type coupling employing aryl boronic acids, providing a three-component assembly of highly substituted pyrroles.

Rhodium(I)-Catalyzed Intermolecular Hydroacylation of α-Keto Amides and Isatins with Non-Chelating Aldehydes

The application of the bidentate, electron-rich bisphosphine ligand, 1,3-bis(dicyclohexyl)phosphine-propane (dcpp), in rhodium(I)-catalyzed intermolecular ketone hydroacylation is herein described. Isatins and α-keto amides are shown to undergo hydroacylation with a variety of non-chelating linear and branched aliphatic aldehydes. Also reported is the synthesis of new bidentate chiral phosphine ligands, and their application in hydroacylation is discussed.

Alkyne hydroacylation: switching regioselectivity by tandem ruthenium catalysis

By using tandem Ru-catalysis, internal alkynes can be coupled with aldehydes for the synthesis of β,γ-unsaturated ketones. The catalyst promotes alkyne transformations with high regioselectivity, with examples that include the differentiation of a methyl vs ethyl substituent on the alkyne. Mechanistic studies suggest that the regioselectivity results from a selective allene formation that is governed by allylic strain.

Metal-free oxidative ipso-carboacylation of alkynes: synthesis of 3-acylspiro[4,5]trienones from N-arylpropiolamides and aldehydes

A general and metal-free radical route to synthesis of 3-acylspiro[4,5]trienones is established that utilizes TBHP (tert-butyl hydrogenperoxide) as an oxidation and a reaction partner to trigger the oxidative ipso-carboacylation of N-arylpropiolamides with aldehydes. This method offers a new difunctionalization of alkynes through oxidative cross coupling of the aldehyde C(sp(2))-H bond with an ipso-aromatic carbon.

Traceless chelation-controlled rhodium-catalyzed intermolecular alkene and alkyne hydroacylation

A new functional-group tolerant, rhodium-catalyzed, sulfide-reduction process is combined with rhodium-catalyzed chelation-controlled hydroacylation reactions to give a traceless hydroacylation protocol. Aryl- and alkenyl aldehydes can be combined with both alkenes, alkynes and allenes to give traceless products in high yields. A preliminary mechanistic proposal is also presented.

Rhodium-catalysed linear-selective alkyne hydroacylation

The use of the electron-rich diphosphine ligand, dcpe, allows the efficient and highly linear selective hydroacylative coupling of aldehydes, including aryl examples, with a range of alkynes.