Kinetic Resolution of Tertiary Allylic Alcohols: Highly Enantioselective Access to Cyclic Ethers Bearing an α-Tetrasubstituted Stereocenter

Iridium-catalyzed enantioselective alkynylation and kinetic resolution of alkyl allylic alcohols

Herein, we report an efficient kinetic resolution of alkyl allylic alcohols enabled by an iridium-catalyzed enantioselective alkynylation of alkyl allylic alcohols with potassium alkynyltrifluoroborates. A wide range of chiral 1,4-enynes bearing various functional groups and unreacted enantioenriched allylic alcohols were obtained with excellent enantioselectivities and high kinetic resolution performance (s-factor up to 922). Additionally, this method is particularly effective for preparing some useful optically pure alkyl allylic alcohols, such as the key components towards the synthesis of prostaglandins and naturally occurring matsutakeols, which are difficult to access via other asymmetric reactions. Mechanistic studies revealed that the efficient kinetic resolution might be due to the significant distinction of the η ²-coordination between the (R)- and (S)-allylic alcohols with the iridium/(phosphoramidite, olefin) complex.

Asymmetric Synthesis of 3,3-Disubstituted Isoindolinones Enabled by Organocatalytic Functionalization of Tertiary Alcohols

An enantioselective intramolecular heterocyclization with in situ generated 3-hydroxyisoindolinone-derived N-acyliminium ions has been successfully accomplished. In the presence of a catalytic amount of a chiral phosphoric acid, functionalized 3,3-disubstituted isoindolinones bearing N-acyl-N,O-acetal moieties were obtained with good yields and a high level of stereocontrol (up to 98:2 er). This efficient method proceeds under mild conditions and exhibits broad scope with respect to both 3-hydroxyisoindolinones and hydroxyl partners.

Chiral Brønsted Acid-Catalyzed Intramolecular Asymmetric Allylic Alkylation of Indoles with Primary Alcohols

Herein, chiral Brønsted acid-catalyzed intramolecular asymmetric allylic alkylation of indoles with allylic primary alcohols is described. The allyl alcohols were directly employed as the allylic precursors in this metal-free protocol, without preactivation or any additional activating reagents. This method provides the convenient synthesis of a broad range of functionalized tetrahydrocarbazoles in excellent yields (≤97%) with good enantioselectivity (≤93% ee). The optimal conditions are compatible for gram-scale reaction.

Palladium-Catalyzed Asymmetric [3 + 2] Annulation of Vinylethylene Carbonates with Alkenes Installed on Cyclic N-Sulfonyl Imines: Highly Enantio- and Diastereoselective Construction of Chiral Tetrahydrofuran Scaffolds Bearing Three Vicinal and Quaternary Stereocenters

A multisubstituted tetrahydrofuran building block bearing three vicinal chiral carbon centers widely exists in a broad spectrum of bioactive natural products, and the development of efficient and convenient methods to establish this skeleton remains a challenging task. Herein, we have developed an efficient method for the construction of significant tetrahydrofuran scaffolds bearing three vicinal and α-quaternary chiral carbon stereocenters through Pd-catalyzed asymmetric [3 + 2] annulation of vinylethylene carbonates with alkenes installed on cyclic N-sulfonyl imines. A series of multisubstituted tetrahydrofuran derivatives are obtained in high efficiencies with excellent enantioselectivities and diastereoselectivities. Density functional theory (DFT) studies are accomplished to rationalize the stereocontrol of the annulation process and disclose that methanol could be applied to stabilize the reactive zwitterionic π-allylpalladium via the H-bond interaction.

Recent Advances in Catalytic Nonenzymatic Kinetic Resolution of Tertiary Alcohols

The kinetic resolution (KR) of racemates is one of the most widely used approaches to access enantiomerically pure compounds. Over the past two decades, catalytic nonenzymatic KR has gained popularity in the field of asymmetric synthesis due to the rapid development of chiral catalysts and ligands in asymmetric catalysis. Chiral tertiary alcohols are prevalent in a variety of natural products, pharmaceuticals, and biologically active chiral compounds. The catalytic nonenzymatic KR of racemic tertiary alcohols is a straightforward strategy to access enantioenriched tertiary alcohols. This short review describes recent advances in catalytic nonenzymatic KR of tertiary alcohols, including organocatalysis and metal catalysis.

1 Introduction

2 Organocatalysis

2.1 Peptide Catalyst

2.2 Chiral Phosphoric Acid Catalyst

2.3 Chiral Lewis Base Catalyst

2.4 Chiral Quaternary Ammonium Salt Catalyst

3 Metal Catalysis

3.1 Mixed La-Li Heterobimetallic Catalyst

3.2 Rh Catalyst

3.3 Hf Catalyst

3.4 Pd Catalyst

3.5 Cu Catalyst

3.6 Ag Catalyst

4 Conclusion and Outlook

Kinetic Resolution of Racemic Tertiary Allylic Alcohols through SN2’ Reaction Using a Chiral Bisphosphoric Acid/Silver(I) Salt Co-catalyst System

A highly efficient kinetic resolution (KR) of racemic tertiary allylic alcohols was achieved through an intramolecular allylic substitution reaction using a co-catalyst system composed of chiral bisphosphoric acid and silver carbonate. This reaction afforded enantioenriched diene monoepoxides along with the recovery of tertiary allylic alcohols in a highly enantioselective manner, realizing an extremely high s-factor in most cases. The present method provides a new access to enantioenriched tertiary allylic alcohols, multifunctional compounds that are applicable for further synthetic manipulations.

A highly efficient KR of racemic tertiary allylic alcohols was developed through the intramolecular S_N2′ reaction using the chiral bisphosphoric acid/silver carbonate co-catalyst system, affording cis-epoxides and recovered alcohols in a high s-factor.

Phosphorus-Based Organocatalysis for the Dehydrative Cyclization of N-(2-Hydroxyethyl)amides into 2-Oxazolines

A metal-free, biomimetic catalytic protocol for the cyclization of N-(2-hydroxyethyl)amides to the corresponding 2-oxazolines (4,5-dihydrooxazoles), promoted by the 1,3,5,2,4,6-triazatriphosphorine (TAP)-derived organocatalyst tris(o-phenylenedioxy)cyclotriphosphazene (TAP-1) has been developed. This approach requires less precatalyst compared to the reported relevant systems, with respect to the phosphorus atom (the maximum turnover number (TON) ∼ 30), and exhibits a broader substrate scope and higher functional-group tolerance, providing the functionalized 2-oxazolines with retention of the configuration at the C(4) stereogenic center of the 2-oxazolines. Widely accessible β-amino alcohols can be used in this approach, and the cyclization of N-(2-hydroxyethyl)amides provides the desired 2-oxazolines in up to 99% yield. The mechanism of the reaction was studied by monitoring the reaction using spectral and analytical methods, whereby an ¹⁸O-labeling experiment furnished valuable insights. The initial step involves a stoichiometric reaction between the substrate and TAP-1, which leads to the in situ generation of the catalyst, a catechol cyclic phosphate, as well as to a pyrocatechol phosphate and two possible active intermediates. The dehydrative cyclization was also successfully conducted on the gram scale.

Asymmetric Synthesis of Spiro[3,2'-morpholine-oxindoles] Derivatives via the [5 + 1] Annulation Reaction

An efficacious method in which BINOL-type chiral imidodiphosphoric acid catalyzed the asymmetric [5 + 1] annulation reaction of 2-pyrrolylphenol with 1-methylindoline-2,3-dione was established. The strategy tolerated a broad substrate scope, and 30 examples were obtained. A range of enantioenriched spiro[3,2'-morpholine-oxindole] derivatives which incorporate a tertiary stereocenter, with moderate to excellent yields (up to 96%) and enantioselectivities (up to 99%) under mild conditions, was delivered.

The Pd-catalysed asymmetric allylic alkylation reactions of sulfamidate imines

The Pd-catalysed asymmetric allylic alkylation (Pd-AAA) of prochiral enamide anions derived from 5H-oxathiazole 2,2-dioxides has been developed. Various 4,5-disubstituted and 4-substituted cyclic sulfamidate imines have participated in the transformation with a range of allyl carbonates-as well as 2-vinyl oxirane, 2-vinyl-N-tosylaziridine, and 2-vinyl-1,1-cyclopropane dicarboxylate-to furnish the desired C-allylated products in moderate to high yields, with high regioselectivites and generally high enantioselectivities. Conversion between N- and C-allyl products was observed, with the N-allylated products converting to the C-allylated products over time. The resulting high-value allylated heterocyclic products all bear a tetrasubstituted stereogenic centre and can be reduced to an allylated chiral sulfamidate or an amino alcohol.

Asymmetric Enamide-Imine Tautomerism in the Kinetic Resolution of Tertiary Alcohols

An efficient protocol for kinetic resolution of tertiary alcohols has been developed through an unprecedented asymmetric enamide-imine tautomerism process enabled by chiral phosphoric acid catalysis. A broad range of racemic 2-arylsulfonamido tertiary allyl alcohols could be kinetically resolved with excellent kinetic resolution performances (with s-factor up to >200). This method is particularly effective for a series of 1,1-dialkyl substituted allyl alcohols, which produced chiral tertiary alcohols that would be difficult to access via other asymmetric methods. Facile and versatile transformations of the chiral α-hydroxy imine and enamide products, especially the efficient stereodivergent synthesis of all four stereoisomers of β-amino tertiary alcohols using one enantiomer of the catalyst, demonstrated the value of this kinetic resolution method.