Parallel kinetic resolution of aziridines via chiral phosphoric acid-catalyzed apparent hydrolytic ring-opening

We report a chiral phosphoric acid catalyzed apparent hydrolytic ring-opening reaction of racemic aziridines in a regiodivergent parallel kinetic resolution manner. Harnessing the acyloxy-assisted strategy, the highly stereocontrolled nucleophilic ring-opening of aziridines with water is achieved. Different kinds of aziridines are applicable in the process, giving a variety of enantioenriched aromatic or aliphatic amino alcohols with up to 99% yields and up to >99.5 : 0.5 enantiomeric ratio. Preliminary mechanistic study as well as product elaborations were inducted as well.

Cobalt Carbonyls Stabilized by N,P-Ligands: Synthesis, Structure, and Catalytic Property for Ethylene Oxide Hydroalkoxycarbonylation

Reactions of N,P-Ligands as Ph₂ P(o-NMe₂ C₆ H₄ ) (¹ L), 2,6-iPr₂ C₆ H₃ NHC(Ph)=NC₆ H₄ (o-PPh₂ ) (² L), and Ph₂ PN(R)PPh₂ (R=iPr (³ L), cyclo-C₆ H₁₁ (⁴ L), tBu (⁵ L), CH₂ C₄ H₇ O (⁶ L)) each with dicobalt octacarbonyl produced complexes [¹ LCo(CO)₃ ]₂ (1), [² LCo(CO)(μ-CO)₂ Co(CO)₃ ] (2), [³ LCo(CO)₃ ]⁺ [Co(CO)₄ ]^- (3), [³ LCo(CO)₂ ]₂ (4), [⁴ LCo(CO)₂ ]₂ (5), [⁵ LCo(CO)₂ ]⁺ [Co(CO)₄ ]^- (6), and [⁶ LCo(CO)₂ ]⁺ [Co(CO)₄ ]^- (7). Complexes 1-7 have all been structurally characterized by X-ray crystallography, IR and NMR spectroscopies, and elemental analysis. Catalytic tests on transformation of ethylene oxide (EO), CO and MeOH into methyl 3-hydroxypropionate (3-HMP) indicate that complexes 1-7 are active, where ion-pair complexes 3 and 6-7 behave more excellently (by achieving 88.4-93.6% 3-HMP yields) than the neutral species 1-2 and 4-5 (35.0-46.5% 3-HMP yields) when the reactions are all operated at 2 MPa CO pressure and 50 °C in MeOH solvent. Density functional theory (DFT) study by selecting 3 as a model suggests a cooperative catalytic reaction mechanism by [Co(CO)₄ ]^- and its counter cation [³ LCo(CO)₃ ]⁺ . The cobalt-homonuclear ion-pair catalyzed hydroalkoxycarbonylation of EO is present herein.

Highly Active Cooperative Lewis Acid-Ammonium Salt Catalyst for the Enantioselective Hydroboration of Ketones

Enantiopure secondary alcohols are fundamental high-value synthetic building blocks. One of the most attractive ways to get access to this compound class is the catalytic hydroboration. We describe a new concept for this reaction type that allowed for exceptional catalytic turnover numbers (up to 15 400), which were increased by around 1.5-3 orders of magnitude compared to the most active catalysts previously reported. In our concept an aprotic ammonium halide moiety cooperates with an oxophilic Lewis acid within the same catalyst molecule. Control experiments reveal that both catalytic centers are essential for the observed activity. Kinetic, spectroscopic and computational studies show that the hydride transfer is rate limiting and proceeds via a concerted mechanism, in which hydride at Boron is continuously displaced by iodide, reminiscent to an SN 2 reaction. The catalyst, which is accessible in high yields in few steps, was found to be stable during catalysis, readily recyclable and could be reused 10 times still efficiently working.

Cationic aluminum, gallium, and indium complexes in catalysis

The introduction of cationic charge allows cationic group 13 complexes to be excellent Lewis acid catalysts. Cationic aluminum, gallium, and indium complexes in catalysis are comprehensively reviewed based on the reaction type.

Catalytic Reactions by Heterobimetallic Carbonyl Complexes with Polar Metal–Metal Interactions

Heterobinuclear catalysts capable of bimetallic cooperative bond activation provide an alternative pathway to approach the discovery of novel and unique reactivity and selectivity in catalytic transformations, complementing more traditional mononuclear precious metal catalysts. This review summarizes recent advances in homogenous catalysis using heterobimetallic carbonyl catalysts with polar metal–metal interactions.

1 Introduction

2 Hydrogenation and Hydrofunctionalization

3 Carbonylation and Carboxylation

4 Oxidative Transformations

5 Conclusion and Outlook

Progress in the Preparation of Functional and (Bio)Degradable Polymers via Living Polymerizations

This review presents the latest developments in (bio)degradable approaches and functional aliphatic polyesters and polycarbonates prepared by typical ring-opening polymerization (ROP) of lactones and trimethylene carbonates. It also considers several recent innovative synthetic methods including radical ring-opening polymerization (RROP), atom transfer radical polyaddition (ATRPA), and simultaneous chain- and step-growth radical polymerization (SCSRP) that produce aliphatic polyesters. With regard to (bio)degradable approaches, we have summarized several representative cleavable linkages that make it possible to obtain cleavable polymers. In the section on functional aliphatic polyesters, we explore the syntheses of specific functional lactones, which can be performed by ring-opening copolymerization of typical lactone/lactide monomers. Last but not the least, in the recent innovative methods section, three interesting synthetic methodologies, RROP, ATRPA, and SCSRP are discussed in detail with regard to their reaction mechanisms and polymer functionalities.

Nucleophilic Transformations of Lewis Acid-Activated Disubstituted Epoxides with Catalyst-Controlled Regioselectivity

Due to their inherent ring strain and electrophilicity, epoxides are highly attractive building blocks for fundamental organic reactions. However, controlling the regioselectivity of disubstituted epoxide transformations is often particularly challenging. Most Lewis acid-mediated processes take advantage of intrinsic steric or electronic substrate bias to influence the site of nucleophilic attack. Therefore, the scope of many of these systems is frequently quite limited. Recent efforts to generate catalysts that can overcome substrate bias have expanded the synthetic utility of these well-known reactions. In this Perspective, we highlight various regioselective transformations of disubstituted epoxides, emphasizing those that have inspired the production of challenging, catalyst-controlled processes.

Synthesis of Enantioenriched Bromohydrins via Divergent Reactions of Racemic Intermediates from Anchimeric Oxygen Borrowing

We report a chiral phosphoric acid catalyzed bromocyclization/regiodivergent reaction of racemic intermediates sequence, which is enabled by anchimeric oxygen borrowing. Different types of alkenes are applicable, and both enantiomers of the bromohydrin products were obtained in generally excellent yields and enantioselectivities. In addition, an example of enantioconvergent synthesis from the two isomeric products is presented.

Nucleophilic ring opening of trans-2,3-disubstituted epoxides to β-amino alcohols with catalyst-controlled regioselectivity

We report the nucleophilic ring opening of unsymmetrical trans-epoxides to β-amino alcohols with catalyst-controlled regioselectivity.

Total synthesis of tetrahydrolipstatin and stereoisomers via a highly regio- and diastereoselective carbonylation of epoxyhomoallylic alcohols

A concise enantioselective synthesis of tetrahydrolipstatin (THL) and seven stereoisomers has been achieved. The synthesis of THL was accomplished in 10 steps and 31% overall yield from an achiral ynone. Key to the success of the approach is the use of a bimetallic [Lewis acid](+)[Co(CO)4](-) catalyst for a late-stage regioselective carbonylation of an enantiomerically pure cis-epoxide to a trans-β-lactone. The success of this route to THL and its stereoisomers also demonstrated the practicality of the carbonylation catalyst for complex molecule synthesis as well as its functional group compatibility.