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

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.

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.

Photoredox activation for the direct β-arylation of ketones and aldehydes

The direct β-activation of saturated aldehydes and ketones has long been an elusive transformation. We found that photoredox catalysis in combination with organocatalysis can lead to the transient generation of 5π-electron β-enaminyl radicals from ketones and aldehydes that rapidly couple with cyano-substituted aryl rings at the carbonyl β-position. This mode of activation is suitable for a broad range of carbonyl β-functionalization reactions and is amenable to enantioselective catalysis.

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.

An N-linked bidentate phosphoramidite ligand (N-Me-BIPAM) for rhodium-catalyzed asymmetric 1,4-addition of arylboronic acids to α,β-unsaturated ketones

A new bidentate phosphoramidite (N-Me-BIPAM) based on Shibasaki's N-linked BINOL was synthesized. This ligand appears to be highly effective for rhodium-catalyzed asymmetric conjugated addition of arylboronic acids to α,β-unsaturated enones. The reaction of ortho-substituted arylboronic acid with acyclic and cyclic enones provides the corresponding products in good yields and enantioselectivities.

Diastereoselective synthesis and coordination chemistry of enantiopure keto-bis-(2-phosphametallocene)s

Enantiopure 2-(chlorocarbonyl)phosphametallocenes [MCp*(2-{COCl}-3,4-Me(2)-5-Ph-PC(4))] (M = Fe, Ru) react with phospholide anions to give 2-phosphametallocene-2'-acylphospholides K[MCp*(2-CO-2'-{3',4'-Me(2)-5'-PhPC(4)}-3,4-Me(2)-5-Ph-PC(4))] (M = Fe, Ru) and these have been converted into keto-bis-(2-phosphametallocene)s through reaction with [FeClCp*(tmeda)]; templation of this process with CuBr gives rise to the C(2)- (or pseudo-C(2)- when M = Ru) symmetric form of [{MCp*(3,4-Me(2)-5-Ph-PC(4))}(2)-2,2'-(CO)] (M = Fe, Ru; Fe, Fe) with high (>95%) diastereoselectivity. X-Ray structures of these ligands coordinated to [RuCp*Cl] and [PtCl(2)] centres show that the spatial orientation of the very flexible keto-bis-(2-phosphametallocene) structure is highly responsive to the coordination sphere of the chelated platinum or ruthenium centre.

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.

A class of benzene backbone-based olefin-sulfoxide ligands for Rh-catalyzed enantioselective addition of arylboronic acids to enones

A class of readily available and easily tunable benzene backbone-based olefin-sulfoxide ligands was developed for the rhodium-catalyzed asymmetric conjugate addition reaction of arylboronic acids to enones with up to 97% yield and 97% ee.

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.