Catalytic Asymmetric Intramolecular Hydroacylation with Rhodium/Phosphoramidite-Alkene Ligand Complexes

Dibenzoazepine hydrazine is a building block for N-alkene hybrid ligands: exploratory syntheses of complexes of Cu, Fe, and Li

The new hydrazine 5H-dibenzo[b,f]azepin-5-amine (2) reacts with P- and Si-electrophiles via deprotonation to afford P(III)-, P(V)-, and TMS-hydrazides 3-8 and with carbonyl electrophiles via acid-free condensation to the N-substituted hydrazones 9-12 that are potential N-alkene ligands. While β-ketohydrazone 9 and α-dihydrazone 10 react with [Mes(Cu)]4, [Cu(NCCCH3)4]2PF6, and FeCl2(THF)1.5 to afford complexes devoid of alkene interaction, [Cu(OTf)]2·C6H6 reacts with the α-keto hydrazone 11 or with N,N dimethyl-hydrazone 12 to form the neutral dimeric Cu(I) complex 18 with bridging Cu(I)-alkene interactions or the tetrahedral cationic complex 19 in which 12 binds as a bidentate hydrazone-alkene ligand, respectively. The surprising stability of the alkene coordination in complexes 18 and 19 prevents substitutions with, e.g., PPh3.

Amide-Directed, Rhodium-Catalyzed Regio- and Enantioselective Hydroacylation of Internal Alkenes with Unfunctionalized Aldehydes

Despite the current progress achieved in asymmetric hydroacylations, highly enantioselective catalytic addition of unfunctionalized aldehydes to internal alkenes remains an unsolved challenge. Here, using a coordination-assisted strategy, we developed a rhodium-catalyzed regio- and enantioselective addition of unfunctionalized aldehydes to internal alkenes such as enamides and β,γ-unsaturated amides. Valuable α-amino ketones and 1,4-dicarbonyl compounds were directly obtained with high enantioselectivity from readily available materials.

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.

Lewis Acid Catalysed Asymmetric One-Carbon Ring-Expansion of Prochiral Cyclobutanones

Enantioselective methylene insertion into prochiral cyclobutanones is described providing access to chiral β-substituted cyclopentanones as important structural motif in synthesis and natural products. Commercially available trimethylsilyl as well as other silyl diazomethanes act as one-carbon synthon and scandium triflate is found to be a potent Lewis acid catalyst. By using bis(oxazoline) ligands, enantioinduction is achieved for a number of β-substituted cyclopentanones including examples bearing all-carbon quaternary stereocentres.

Asymmetric addition of an N-methyl C(sp3)-H bond to cyclic alkenes enabled by an iridium/phosphine-olefin catalyst

Iridium-catalyzed asymmetric C-H addition of an N-methyl group on 3-trifluoromethyl-2-(N-methylamino)pyridine to cyclic alkenes was realized by using a phosphine-olefin ligand. Indene and its 7-substituted derivatives, acenaphthylene, and some bicyclic alkenes underwent the addition to give the corresponding products in good yields with high enantioselectivity.

Iridium-catalysed branched-selective hydroacylation of 1,3-dienes with salicylaldehydes

Herein, we report an iridium-catalyzed branched-selective hydroacylation of 1-aryl 1,3-dienes with salicylaldehydes under mild conditions with no need of phosphine ligands. With this protocol, a series of α-branched β,γ-unsaturated o-hydroxyacetophenones with biological potentials were synthesized in high efficiency with excellent regioselectivities. When simple 1,3-butadiene or isoprene instead of 1-aryl 1,3-dienes were used, exclusive linear-selective hydroacylation products were obtained.

Synthesis of Axially Chiral Olefin-Oxazoline Ligands via Pd-Catalyzed Multiple C-H Functionalization

We report herein the Pd-catalyzed oxazoline-directed C-H olefination of the N-arylindole skeleton, affording two diastereomers of axially chiral olefin-oxazoline ligands in a one-step procedure. Modifications at the 3- and 3'-positions were facilely achieved via electrophilic substitution of the indole fragment and subsequent oxazoline-directed C-H amidation or olefination of the arene fragment.

Enantioselective Cobalt-Catalyzed Intermolecular Hydroacylation of 1,6-Enynes

We report a cobalt-catalyzed hydroacylation of 1,6-enynes with exogenous aldehydes in a domino sequence to construct enantioenriched ketones. The products were obtained in good yields with excellent regio-, diastereo-, and enantioselectivity. Furthermore, the chiral products served as valuable precursors to access complex spirocyclic scaffolds with three contiguous stereocenters. The asymmetric hydroacylation process exhibited no C-H crossover and no KIE, thus indicating that the C-H bond cleavage was not involved in the turnover-limiting step.

Palladium-Catalyzed Amination/Dearomatization Reaction of Indoles and Benzofurans

This report describes a palladium-catalyzed dearomatization and amination tandem reaction of 2,3-disubstituted indoles and benzofurans via the Catellani strategy. This reaction provides a new method for the construction of amino-substituted indoline-fused cyclic and benzofuran spiro compounds in good yields. The reaction has broad functional group compatibility and substrate scope.

Rhodium-Catalyzed Asymmetric Addition of Organoboronic Acids to Aldimines Using Chiral Spiro Monophosphite-Olefin Ligands: Method Development and Mechanistic Studies

The synthesis of a novel type of chiral spiro monophosphite-olefin (SMPO) ligands based on a hexamethyl-1,1'-spirobiindane scaffold was accomplished starting from Bisphenol C. The optimal ligand could serve as an elegant chiral bidentate ligand in the Rh-catalyzed asymmetric 1,2-addition of organoboronic acids to various acyclic/cyclic aldimines, leading to chiral amines with high yields and excellent enantioselectivities. Detailed stereochemical models for enantioselective induction were elucidated through DFT calculations and postulated the origins of the higher enantioselectivity of phosphite-olefin ligands.

Catalytic, Enantioselective Synthesis of Polycyclic Nitrogen, Oxygen, and Sulfur Heterocycles via Rh-Catalyzed Alkene Hydroacylation

Enantioselective synthesis of polycyclic nitrogen, oxygen, and sulfur heterocycles by rhodium-catalyzed intramolecular alkene hydroacylation is reported. The intramolecular hydroacylation reactions generate 1,4-dihydrocyclopenta[b]indol-3(2H)-ones and 3,4-dihydrocyclopenta[b]indol-1(2H)-one in moderate-to-high yields (65-99%) with good-to-excellent enantioselectivities (84-99% ee). The catalyst system also promotes alkene hydroacylation of 3-vinylfuran-, 3-vinylbenzothiophene-, and 3-vinylthiophene-2-carboxaldehydes to generate the corresponding ketone products in moderate-to-high yields (71-91% yield) with excellent enantioselectivities (97-99% ee).

Enantioselective CuH-Catalyzed Hydroacylation Employing Unsaturated Carboxylic Acids as Aldehyde Surrogates

The direct asymmetric copper hydride (CuH)-catalyzed coupling of α,β-unsaturated carboxylic acids to aryl alkenes to access chiral α-aryl dialkyl ketones is reported. A variety of substrate substitution patterns, sensitive functional groups, and heterocycles are tolerated in this reaction, which significantly expands the range of accessible products compared with existing hydroacylation methodology. Although mechanistic studies are ongoing, we propose that CuH-catalyzed silylation of unsaturated acids occurs to access a uniquely effective acyl electrophilic coupling partner.

Intermolecular Markovnikov-Selective Hydroacylation of Olefins Catalyzed by a Cationic Ruthenium-Hydride Complex

The cationic Ru-H complex was found to be an effective catalyst for the intermolecular hydroacylation of aryl-substituted olefins with aldehydes to form branched ketone products. The preliminary kinetic and spectroscopic studies elucidated a ruthenium-acyl complex as the key intermediate species. The catalytic method directly afforded branched ketone products in a highly regioselective manner while tolerating a number of heteroatom functional groups.

Rh-Catalyzed Stereospecific Synthesis of Allenes from Propargylic Benzoates and Arylboronic Acids

An enantiospecific approach to the synthesis of optically active, trisubstituted allenes from chiral propargylic benzoates and arylboronic acids has been developed. The transformation is catalyzed by a Rh-(P,olefin) complex formed in situ from [{Rh(cod)Cl}2] and a readily available phosphoramidite ligand. The method furnishes an assortment of diverse allenes in high yields and excellent enantiospecificity under mild conditions.

Diastereoselective Radical Hydroacylation of Alkylidenemalonates with Aliphatic Aldehydes Initiated by Photolysis of Hypervalent Iodine(III) Reagents

Diastereoselective radical hydroacylation of chiral alkylidenemalonates with aliphatic aldehydes is realized by the combination of a hypervalent iodine(III) reagent and UV-light irradiation. The reaction is initiated by the photolysis of hypervalent iodine(III) reagents under mild, metal-free conditions, and is the first example of diastereoselective addition of acyl radicals to olefins to afford chiral ketones in a highly stereoselective fashion. The obtained optically active ketones are useful chiral synthons, as exemplified by the short formal synthesis of (-)-methyleneolactocin.

Rh-Catalyzed Desymmetrization of α-Quaternary Centers by Isomerization-Hydroacylation

We describe a Rh-catalyzed desymmetrization of all-carbon quaternary centers from α,α-bis(allyl)aldehydes by a cascade featuring isomerization and hydroacylation. This desymmetrization competes with two other novel olefin functionalizations that are triggered by C-H bond activation, including carboacylation and bisacylation. A BIPHEP ligand promotes enantioselective formation of α-vinylcyclopentanones. Mechanistic studies support irreversible and enantioselective olefin-isomerization followed by olefin-hydroacylation.

Enantioselective hydroacylation of olefins with rhodium catalysts

Over thirty years ago, James and Young reported the first enantioselective olefin hydroacylation by using rhodium catalysts. This viewpoint highlights the advances in this area, including 4-pentenal cyclisations, medium-ring syntheses, and intermolecular variants.

Stereoselective hydroacylation of bicyclic alkenes with 2-hydroxybenzaldehydes catalyzed by hydroxoiridium/diene complexes

A hydroxoiridium complex coordinated with 1,5-cyclooctadiene efficiently catalyzed the hydroacylation of bicyclic alkenes with 2-hydroxybenzaldehyde and its derivatives in high yields with high stereoselectivity.

Asymmetric synthesis of axially chiral anilides by Pd-catalyzed allylic substitutions with P/olefin ligands

Palladium-catalyzed allylic substitutions of ortho-substituted anilides using P/olefin ligands were achieved to afford chiral anilides with up to 84% ee.

Enantioselective synthesis of polycyclic nitrogen heterocycles by Rh-catalyzed alkene hydroacylation: constructing six-membered rings in the absence of chelation assistance

Catalytic, enantioselective hydroacylations of N-allylindole-2-carboxaldehydes and N-allylpyrrole-2-carboxaldehydes are reported. In contrast to many alkene hydroacylations that form six-membered rings, these annulative processes occur in the absence of ancillary functionality to stabilize the acylrhodium(III) hydride intermediate. The intramolecular hydroacylation reactions generate 7,8-dihydropyrido[1,2-a]indol-9(6H)ones and 6,7-dihydroindolizin-8(5H)-ones in moderate to high yields with excellent enantioselectivities.