Biocatalysis has emerged as a greener alternative to traditional organic synthesis, with transaminases excelling in chiral amine production. However, traditional optimization methods are often labor-intensive due to the complexity of interdependent parameters and limited kinetic insights. This study highlights the integration of Raman-based Process Analytical Technology (PAT) and kinetic modeling for real-time monitoring and rapid optimization of a challenging biocatalytic transamination. A modified Michaelis–Menten model, accounting for enzyme denaturation and substrate degradation, was developed to reasonably predict yields over time. Using minimal 3-5 experiments, conditions were optimized to reduce enzyme loading and improve reaction volumes. Key kinetic parameters, such as enzyme denaturation and substrate degradation half-life, were extrapolated and validated. Yield predictions were validated through multi-gram scale reactions, with the product isolated at 96:4 enantiomeric ratio (er) via direct salt binding under optimized conditions.

Chiral Ni-PHOX complexes in combination with photoredox catalysis are shown to be effective to achieve the asymmetric coupling of amino acids with 2-iodopyridines at the C2-position. The regio- and enantioselective protocol developed herein enables direct access to chiral pyrid-2-yl beta-aminoalcohols, which are found in many active pharmaceutical ingredients. This methodology can be extended to other heteroarenes, such as quinolines and azines, on one gram scale. Computational studies supported by experimentation revealed the trend of ligand steric and electronic influences on enantioselectivity. A plausible mechanism was proposed using DFT to further rationalize the observed regio- and enantioselectivity.

This Perspective is part of a continuing review series that is published within the alliance among AbbVie, Boehringer Ingelheim, and Pfizer. The purpose of this article is to highlight the myriad of applications for nonprecious metal catalysts, specifically highlighting copper, cobalt, iron, and nickel. The utility of these metals, alongside their low cost and sustainable feedstocks, makes them ideal reagents. To underscore the advantages of nonprecious metal catalysis, we have highlighted transformations that are of interest to synthetic chemists.

Synthesis of molecules containing all-carbon quaternary stereocenters has been a longstanding challenge in organic chemistry. In one of our discovery oncology programs, a key chiral building block bearing an all-carbon quaternary chiral center was of particular interest and was later identified as a core structure for a KRAS G12C inhibitor. Herein, the development of a safer and practical route to the key building block 1 is described. By replacing processes involving the use of an energetic reagent and extensive chromatographic purifications, a scalable process utilizing chemical resolution was developed to access the chiral building block in kilogram quantities, enabling timely delivery of API for preclinical and clinical studies.

Commercially and readily available MSTFA [2,2,2-trifluoro-N-methyl-N-(trimethylsilyl)acetamide] was identified as a highly effective TMS (trimethylsilyl) source for the convenient preparation of cyclic acetals under modified Noyori's conditions. The reactions proceeded smoothly under mild conditions, affording a wide range of the corresponding cyclic acetals with excellent yields in the presence of catalytic TMSOTf (trimethylsilyl trifluoromethanesulfonate). The present method does not require a large excess of diols that can be valuable and does not require presynthesized silylated diols. In contrast to other silylating reagents such as BSA [N,O-bis(trimethylsilyl)acetamide] and BSTFA [N,O-bis(trimethylsilyl)trifluoroacetamide], the application of MSTFA avoided the inhibition of catalytic acetalization by the side product 2,2,2-trifluoro-N-methylacetamide.

A short and scalable process for the facile synthesis of chiral spirocyclic isoxazolone 1 was developed and demonstrated on a multiple kilogram scale in four steps from a readily available starting material 8. To achieve process sustainability and efficiency, we implemented a highly efficient catalytic asymmetric allylic alkylation and a telescopic chemical process. More than 160 kg of the spirocyclic isoxazolone 1 were produced as a crystalline solid by a simple operation with >99:1 er and 38% overall yield. The structure of 1 was further confirmed by single-crystal X-ray analysis.

Asymmetric allylic alkylation (AAA) presents an exceptionally powerful and efficient tool for the rapid synthesis of a diverse range of chiral compounds with high yields and excellent levels of enantioselectivity. To support the production of ethyl (R)-1-allyl-2-oxocyclohexane-1-carboxylate 1 on a large scale, a highly practical and economical AAA process is highly desirable. Herein, we report a greatly improved reaction protocol by thorough optimization of the original conditions developed by Trost et al. Multiple reaction parameters including reaction temperature, concentration, stoichiometric amount of TMG (1,1,3,3-tetramethylguanidine), and water are thoroughly investigated. It was determined that the reaction rate was significantly improved in the presence of 2.0 equiv of TMG and an optimal amount of water (Pd:H2O = 1:160) at 10–15 °C. Our efforts led to the design and development of a highly efficient chemical process using [η3-C3H5PdCl]2 as low as 0.025 mol % under solvent-free conditions, enabling facile and robust scaleup in an economical and sustainable fashion on a large scale.

An improved chemical process has been developed for the synthesis of (S,S)-DACH-Ph Trost ligand. The amidation of 2-diphenylphosphinylbenzoic acid and (S,S)-diaminocyclohexarie is promoted by stoichiometric CDI and catalytic imidazole hydrochloride. The resulting product, (S,S)-DACH-Ph Trost ligand, is isolated as a white solid in 80% yield with >99% ee by simple filtration without column chromatography. The current facile process is also demonstrated on kilogram scale.

A mild and nonreversible tert-butylation of alcohols and phenols can be achieved in high yields using the noncoordinating acid-base catalyst [bis(trifluoromethane)sulfonimide and 2,6-lutidine] with a tert-butylation reagent, tert-butyl 2,2,2-trichloroacetimidate. This method allows the use of substrates containing acid sensitive groups such as ketal, Boc, and boronate esters.

Enantioselective synthesis of α-aryl and α-heteroaryl piperidines is reported. The key step is an iridium-catalyzed asymmetric hydrogenation of substituted N-benzylpyridinium salts. High levels of enantioselectivity up to 99.3:0.7 er were obtained for a range of α-heteroaryl piperidines. DFT calculations support an outersphere dissociative mechanism for the pyridinium reduction. Notably, initial protonation of the final enamine intermediate determines the stereochemical outcome of the transformation rather than hydride reduction of the resultant iminium intermediate.

A practical, efficient and broadly applicable catalytic method for synthesis of easily differentiable vicinal diboronate compounds is presented. Reactions are promoted by a combination of PCy3 or PPh3, CuCl and LiOt-Bu and may be performed with readily accessible alkenyl boronate substrates. Through the use of an alkenyl-B(pin) (pin = pinacolato) or alkenyl-B(dan) (dan = naphthalene-1,8-diaminato) starting material and commercially available (pin)B-B(dan) or B-2(pin)(2) as the reagent, a range of vicinal diboronates, including those that contain a B-substituted quaternary carbon center, may be prepared in up to 91% yield and with >98% site selectivity. High enantioselectivities can be obtained (up to 96:4 er) through the use of commercially available chiral bis-phosphine ligands for reactions that afford mixed diboronate products. (C) 2017 Elsevier Ltd. All rights reserved.

A rapidly emerging set of catalytic reactions involves intermediates that contain a copper-substituted stereogenic carbon centre. Here, we demonstrate that an intimate understanding of this distinction provides ways for addressing limitations in reaction scope and explaining why unexpected variations in enantioselectivity often occur. By using catalytic enantioselective Cu-boryl addition to alkenes as the model process, we elucidate several key mechanistic principles. We show that higher electrophile concentration can lead to elevated enantioselectivity. This is because diastereoselective Cu-H elimination may be avoided and/or achiral Cu-boryl intermediates can be converted to allyl-B(pin) rather than add to an alkene. We illustrate that lower alkene amounts and/or higher chiral ligand concentration can minimize the deleterious influence of achiral Cu-alkyl species, resulting in improved enantiomeric ratios. Moreover, and surprisingly, we find that enantioselectivities are higher with the less reactive allylphenyl carbonates as chemoselective copper-hydride elimination is faster with an achiral Cu-alkyl species.

An entry from the Cambridge Structural Database, the world’s repository for small molecule crystal structures. The entry contains experimental data from a crystal diffraction study. The deposited dataset for this entry is freely available from the CCDC and typically includes 3D coordinates, cell parameters, space group, experimental conditions and quality measures.

Broadly applicable enantioselective C-B and C-Si bond-forming processes catalyzed by an N-heterocyclic carbene (NHC) were recently introduced; these boryl and silyl conjugate addition reactions (BCA and SCA, respectively), which proceed without the need for a transition-metal complex, represent reaction pathways that are distinct from those facilitated by transition-metal-containing species (e.g., Cu, Ni, Pt, Pd, or Rh based). The Lewis-base-catalyzed (NHC) transformations are valuable to chemical synthesis, as they can generate high enantioselectivities and possess unique chemoselectivity profiles. Here, the results of investigations that elucidate the principal features of the NHC-catalyzed BCA and SCA processes are detailed. Spectroscopic evidence is provided illustrating why the presence of excess base and MeOH or H2O is required for efficient and enantioselective boryl and silyl addition reactions. It is demonstrated that the proton sources influence the efficiency and/or enantioselectivity of NHC-catalyzed enantioselective transformations in several ways. The positive, and at times adverse, impact of water (biphasic conditions) on catalytic enantioselective silyl addition reactions is analyzed. It is shown that a proton source can facilitate nonenantioselective background reactions and NHC decomposition, requiring the catalyst to surpass such complications. Stereochemical models are presented that account for the identity of the observed major enantiomers, providing a rationale for the differences in selectivity profiles of BCA and SCA processes.

The first examples of Lewis base catalyzed enantioselective boryl conjugate additions (BCAs) that generate products containing boron-substituted quaternary carbon stereogenic centers are disclosed. Reactions are performed in the presence of 1.0-5.0 mol% of a readily accessible chiral accessible N-heterocyclic carbene (NHC) and commercially available bis(pinacolato)diboron; cyclic or linear α,β-unsaturated ketones can be used and rigorous exclusion of air or moisture is not necessary. The desired products are obtained in 63-95% yield and 91:9 to >99:1 enantiomeric ratio (e.r.). The special utility of the NHC-catalyzed approach is demonstrated in the context of an enantioselective synthesis of natural product antifungal (-)-crassinervic acid.

The first broadly applicable metal-free enantioselective method for boron conjugate addition (BCA) to α,β-unsaturated carbonyls is presented. The C-B bond forming reactions are promoted in the presence of 2.5-7.5 mol % of a readily accessible C(1)-symmetric chiral imidazolinium salt, which is converted, in situ, to the catalytically active diastereo- and enantiomerically pure N-heterocyclic carbene (NHC) by the common organic base 1,8-diazabicyclo[5.4.0]undec-7-ene (dbu). In addition to the commercially available bis(pinacolato)diboron [B(2)(pin)(2)], and in contrast to reactions with the less sterically demanding achiral NHCs, the presence of MeOH is required for high efficiency. Acyclic and cyclic α,β-unsaturated ketones, as well as acyclic esters, Weinreb amides, and aldehydes, can serve as suitable substrates; the desired β-boryl carbonyls are isolated in up to 94% yield and >98:2 enantiomer ratio (er). Transformations are often carried out at ambient temperature. In certain cases, such as when the relatively less reactive unsaturated amides are used, elevated temperatures are required (50-66 °C); nonetheless, reactions remain highly enantioselective. The utility of the NHC-catalyzed method is demonstrated through comparison with the alternative Cu-catalyzed protocols; in cases involving a polyfunctional substrate, unique profiles in chemoselectivity are exhibited by the metal-free approach (e.g., conjugate addition vs reaction with an alkyne, allene, or aldehyde).

Novel intermolecular and intramolecular generations of ortho-quinone methides and their formal [4+2]-cycloaddition reactions with olefins catalyzed by PtCl4 and AuCl3 under mild conditions have been developed. Good to excellent yields (up to 99%) and diastereoselectivity (up to >99:1) of the chromans were obtained. PtCl4 was found to be effective and compatible with various functional groups present in the substrates. A mechanism accounting for its catalytic cycle is proposed and discussed.