Vicinal-Diamine-Based Chiral Chain Dienes as Ligands for Rhodium(I)-Catalyzed Highly Enantioselective Conjugated Additions

Enzymatic Assembly of Diverse Lactone Structures: An Intramolecular C-H Functionalization Strategy

Lactones are cyclic esters with extensive applications in materials science, medicinal chemistry, and the food and perfume industries. Nature's strategy for the synthesis of many lactones found in natural products always relies on a single type of retrosynthetic strategy, a C-O bond disconnection. Here, we describe a set of laboratory-engineered enzymes that use a new-to-nature C-C bond-forming strategy to assemble diverse lactone structures. These engineered "carbene transferases" catalyze intramolecular carbene insertions into benzylic or allylic C-H bonds, which allow for the synthesis of lactones with different ring sizes and ring scaffolds from simple starting materials. Starting from a serine-ligated cytochrome P450 variant previously engineered for other carbene-transfer activities, directed evolution generated a variant P411-LAS-5247, which exhibits a high activity for constructing a five-membered ε-lactone, lactam, and cyclic ketone products (up to 5600 total turnovers (TTN) and >99% enantiomeric excess (ee)). Further engineering led to variants P411-LAS-5249 and P411-LAS-5264, which deliver six-membered δ-lactones and seven-membered ε-lactones, respectively, overcoming the thermodynamically unfavorable ring strain associated with these products compared to the γ-lactones. This new carbene-transfer activity was further extended to the synthesis of complex lactone scaffolds based on fused, bridged, and spiro rings. The enzymatic platform developed here complements natural biosynthetic strategies for lactone assembly and expands the structural diversity of lactones accessible through C-H functionalization.

Chiral Diene Ligands in Asymmetric Catalysis

Asymmetric catalysis has emerged as a general and powerful approach for constructing chiral compounds in an enantioselective manner. Hence, developing novel chiral ligands and catalysts that can effectively induce asymmetry in reactions is crucial in modern chemical synthesis. Among such chiral ligands and catalysts, chiral dienes and their metal complexes have received increased attention, and a great progress has been made over the past two decades. This review provides comprehensive and critical information on the essential aspects of chiral diene ligands and their importance in asymmetric catalysis. The literature covered ranges from August 2003 (when the first effective chiral diene ligand for asymmetric catalysis was reported) to October 2021. This review is divided into two parts. In the first part, the chiral diene ligands are categorized according to their structures, and their preparation methods are summarized. In the second part, their applications in asymmetric transformations are presented according to the reaction types.

An azo-bridged ring system enabled by-standing immobilization of a chiral diene ligand

A family of 9-azabicyclo[3.3.1]nonadiene ligands were developed, and the nitrogen atom in the bridged ring enables a facile immobilization of diene ligands to silica.

Electronic and Steric Tuning of an Atropisomeric Disulfoxide Ligand Motif and Its Use in the Rh(I)-Catalyzed Addition Reactions of Boronic Acids to a Wide Range of Acceptors

A novel chiral disulfoxide ligand pair bearing fluorine atoms at the 6 and 6' position of its atropisomeric backbone, ( M, S, S)- and ( P, S, S)- p-Tol-6F-BIPHESO, was synthesized. Complexation to a rhodium(I) precursor gave rise to μ-Cl- and μ-OH-bridged rhodium dimer complexes incorporating the new ( M, S, S)- p-Tol-6F-BIPHESO ligand, while its sibling ( P, S, S)- p-Tol-6F-BIPHESO was not complexed efficiently to the rhodium precursor. The performance of this disulfoxide ligand [( M, S, S)- p-Tol-6F-BIPHESO] in catalysis was tested in both 1,4- and 1,2-addition reactions of arylboronic acids. We show that addition to both cyclic and acyclic enones as well as N-tosylarylimines proceeds with high yields and high enantioselectivities to give the corresponding products. The synthesis of enantiomerically pure p-Tol-6F-BIPHESO is straightforward and inexpensive which, together with the high catalytic performance and wide substrate scope for these addition reactions, makes it a very attractive alternative to more classical chiral ligand entities.

Chemoselective α-Methylenation of Aromatic Ketones Using the NaAuCl4/Selectfluor/DMSO System

Gold-catalyzed chemoselective α-methylenation of aromatic ketones was developed through the use of Selectfluor as a methylenating agent. A variety of useful 1,2-disubstituted propenone derivatives can be prepared in good yields via the present protocol. This reaction features a simple operation, good functional group tolerance, and broad scope of substrates.

Chiral ligands designed in China

Asymmetric catalysis has become an indispensable and productive field within the Chinese organic chemistry society. The design of chiral ligands is one of the most prominent research areas in this field. Since the late 1990s, Chinese organic chemists have developed numerous chiral ligands possessing novel chiral skeletons and design concepts. Some of these ligands have been widely adopted and can be regarded as ‘privileged ligand’, which have shown excellent performance in many asymmetric catalytic reactions. In this review, we provide an overview of the chiral ligands designed by Chinese scientists with the aim of promoting the development of this area in China and with the hope of encouraging more scientists across the world to use these ligands when designing asymmetric reactions.

Two phenyls are better than one or three: synthesis and application of terminal olefin-oxazoline (TOlefOx) ligands

A novel terminal olefin-oxazoline ligand was introduced into rhodium-catalyzed asymmetric conjugate addition of arylboronic acids to enones and gave excellent enantioselectivities. The two phenyls proved better than one or three in ligand evaluations.

Rhodium and copper-catalyzed asymmetric conjugate addition of alkenyl nucleophiles

Since the initial reports in the mid-90s, metal catalyzed asymmetric conjugate addition (ACA) reactions evolved as an important tool for the synthetic chemist. Most of the research efforts have been done in the field of rhodium and copper catalyzed ACA reactions employing aryl and alkyl nucleophiles. Despite the great synthetic value of the double bond, the addition of alkenyl nucleophiles remains insufficiently explored. In this account, an overview of the developments in the field of rhodium and copper catalyzed ACA reactions with organometallic alkenyl reagents (B, Mg, Al, Si, Zr, Sn) will be provided. The account is intended to give a comprehensive overview of all the existing methods. However, in many cases only selected examples are displayed in order to facilitate comparison of different ligands and methodologies.

Pd-catalyzed asymmetric allylic alkylations of 3-substituted indoles using chiral P/olefin ligands

A palladium-catalyzed asymmetric allylic alkylation of 3-substituted indoles using P/olefin ligands was successfully achieved to afford a variety of indolenines containing a quaternary carbon stereocenter in high yields with up to 87% ee. Significantly, this reaction provides a concise access to a stereoisomer of the natural product Angelicastigmin.

Binaphthol-catalyzed asymmetric conjugate arylboration of enones

Conjugate addition of arylboronates to α,β-unsaturated ketones may be catalyzed by chiral binaphthols with enantioselectivities of up to 99:1. Best results were observed with 3,3'-dichloro-BINOL. This chemistry was applied to syntheses of intermediates for syntheses of (+)-indatraline and (+)-tolterodine.

Recent advances in transition metal-catalyzed sp3 C-H amination adjacent to double bonds and carbonyl groups

Transition metal-catalyzed C-H amination at positions adjacent to double bonds and carbonyl groups is discussed in this critical review. While the focus will center on the recent developments of α-oxidative amination, some historical developments and mutually beneficial reports in the broader field of C-H amination will be discussed. C-H amination has become a viable method for the efficient installation of nitrogen atoms en route to target molecules (89 references).

Chiral N-tert-butanesulfinyl α,β-unsaturated ketimine: a simple and highly effective olefin/sulfinimide hybrid ligand for asymmetric 1,4-additions

One novel type of chiral olefin/sulfinimide hybrid ligands has been developed through a simple one-step condensation of α,β-unsaturated ketones with tert-butanesulfinamide and utilized successfully for rhodium-catalyzed asymmetric conjugated additions to furnish the desired adducts in high yields with excellent ee's.

Design of chiral sulfoxide-olefins as a new class of sulfur-based olefin ligands for asymmetric catalysis

The design and development of a novel class of chiral sulfur-olefin hybrid ligands with high synthetic feasibility are described. These new sulfoxide-olefin ligands showed excellent catalytic activities and enantioselectivities (up to 98% ee) in rhodium-catalyzed asymmetric 1,4-addition reactions of aryl boronic acids to α,β-unsaturated carbonyl compounds.

Sulfoxide-alkene hybrids: a new class of chiral ligands for the Hayashi-Miyaura reaction

Sulfoxide-alkene hybrids are introduced as a new class of chiral heterodentate ligands for the Hayashi-Miyaura reaction. The synthesis of these ligands was achieved without the use of protecting groups. A chiral resolution was performed via simple column-chromatographic separation of the diastereomeric ligands. Both diastereomers proved to be excellent ligands in Rh-catalyzed 1,4-addition reactions, furnishing chiral products with high enantioselectivities and, remarkably, opposite stereoconfigurations.

Highly enantioselective and efficient synthesis of flavanones including pinostrobin through the rhodium-catalyzed asymmetric 1,4-addition

An efficient synthesis of bioactive chiral flavanones (1) was achieved through the Rh-catalyzed asymmetric 1,4-addition of arylboronic acid to chromone. The reaction in toluene proceeded smoothly at room temperature in the presence of 0.5% Rh catalyst with electron-poor chiral diphosphine MeO-F(12)-BIPHEP. In this reaction, the 1,2-addition to (S)-1 frequently occurred to yield (2S,4R)-2,4-diaryl-4-chromanol as a byproduct, which could be reduced by changing the reaction solvent to CH(2)Cl(2) to deactivate the Rh catalyst (3% required).

α,β-Divinyl tetrahydropyrroles as chiral chain diene ligands in rhodium(I)-catalyzed enantioselective conjugated additions

A series of α,β-divinyl tetrahydropyrroles, synthesized by asymmetric allylic C-H bond activation/conjugated diene addition reaction of ene-2-dienes, were found to be very efficient chiral chain diene ligands in the rhodium-catalyzed conjugated addition of organoboronic acids to various α,β-unsaturated compounds, achieving the desired chiral adducts with good to excellent yields and ee values.