Stereoselective amino alcohol synthesis via chemoselective electrocatalytic radical cross-couplings.

Amino alcohols are vital in natural products, pharmaceuticals and agrochemicals, and as key building blocks for various applications. Traditional synthesis methods often rely on polar bond retrosynthetic analysis, requiring extensive protecting group manipulations that complicate direct access. Here we show a streamlined approach using a serine-derived chiral carboxylic acid in stereoselective electrocatalytic decarboxylative transformations, enabling efficient access to enantiopure amino alcohols.

Discovery of N-X anomeric amides as electrophilic halogenation reagents.

Electrophilic halogenation is a widely used tool employed by medicinal chemists to either pre-functionalize molecules for further diversity or incorporate a halogen atom into drugs or drug-like compounds to solve metabolic problems or modulate off-target effects. Current methods to increase the power of halogenation rely on either the invention of new reagents or activating commercially available reagents with various additives such as Lewis or Brønsted acids, Lewis bases and hydrogen-bonding activators. There is a high demand for new reagents that can halogenate otherwise unreactive compounds under mild conditions.

Scalable Electrochemical Decarboxylative Olefination Driven by Alternating Polarity.

A mild, scalable (kg) metal-free electrochemical decarboxylation of alkyl carboxylic acids to olefins is disclosed. Numerous applications are presented wherein this transformation can simplify alkene synthesis and provide alternative synthetic access to valuable olefins from simple carboxylic acid feedstocks. This robust method relies on alternating polarity to maintain the quality of the electrode surface and local pH, providing a deeper understanding of the Hofer-Moest process with unprecedented chemoselectivity.

Overcoming the limitations of Kolbe coupling with waveform-controlled electrosynthesis.

The Kolbe reaction forms carbon-carbon bonds through electrochemical decarboxylative coupling. Despite more than a century of study, the reaction has seen limited applications owing to extremely poor chemoselectivity and reliance on precious metal electrodes. In this work, we present a simple solution to this long-standing challenge: Switching the potential waveform from classical direct current to rapid alternating polarity renders various functional groups compatible and enables the reaction on sustainable carbon-based electrodes (amorphous carbon).

Chemoselective (Hetero)Arene Electroreduction Enabled by Rapid Alternating Polarity.

Conventional chemical and even electrochemical Birch-type reductions suffer from a lack of chemoselectivity due to a reliance on alkali metals or harshly reducing conditions. This study reveals that a simpler avenue is available for such reductions by simply altering the waveform of current delivery, namely rapid alternating polarity (rAP). The developed method solves these issues, proceeding in a protic solvent, and can be easily scaled up without any metal additives or stringently anhydrous conditions.

Scalable Flow Electrochemical Alcohol Oxidation: Maintaining High Stereochemical Fidelity in the Synthesis of Levetiracetam.

An electrochemical flow process has been developed for an alcohol oxidation step in the synthesis of the generic epilepsy drug levetiracetam. A crucial metric in this process is the retention of high enantiomeric purity as the oxidation of the primary alcohol to the carboxylic acid proceeds via an epimerizable aldehyde intermediate. Here, three different reactor configurations are compared: undivided batch, undivided flow, and divided flow cells.

Expanding the Repertoire for "Large Small Molecules": Prodrug ABBV-167 Efficiently Converts to Venetoclax with Reduced Food Effect in Healthy Volunteers.

Since gaining approval for the treatment of chronic lymphocytic leukemia (CLL), the BCL-2 inhibitor venetoclax has transformed the treatment of this and other blood-related cancers. Reflecting the large and hydrophobic BH3-binding groove within BCL-2, venetoclax has significantly higher molecular weight and lipophilicity than most orally administered drugs, along with negligible water solubility. Although a technology-enabled formulation successfully achieves oral absorption in humans, venetoclax tablets have limited drug loading and therefore can present a substantial pill burden for patients in high-dose indications.

Sequential Reduction of Nitroalkanes Mediated by CS and Amidine/Guanidine Bases: A Controllable Nef Reaction.

In this letter, we describe a mild, functional group-tolerant reductive Nef reaction that utilizes CS and an amidine or guanidine base to sequentially cleave N-O bonds. These conditions transform secondary nitroalkanes to ketones via an isolable oxime with minimal erosion at labile stereogenic carbons, show excellent compatibility with groups sensitive to oxidizing or reducing conditions, display good scalability, and are well-suited for generating useful 3-pyrrolidinone motifs from readily accessible 1,3-dipolar cycloaddition products.

A Laser Driven Flow Chemistry Platform for Scaling Photochemical Reactions with Visible Light.

Visible-light-promoted organic reactions can offer increased reactivity and selectivity via unique reaction pathways to address a multitude of practical synthetic problems, yet few practical solutions exist to employ these reactions for multikilogram production. We have developed a simple and versatile continuous stirred tank reactor (CSTR) equipped with a high-intensity laser to drive photochemical reactions at unprecedented rates in continuous flow, achieving kg/day throughput using a 100 mL reactor. Our approach to flow reactor design uses the Beer-Lambert law as a guideline to optimize catalyst concentration and reactor depth for maximum throughput.

Macrocyclic bis-thioureas catalyze stereospecific glycosylation reactions.

Carbohydrates are involved in nearly all aspects of biochemistry, but their complex chemical structures present long-standing practical challenges to their synthesis. In particular, stereochemical outcomes in glycosylation reactions are highly dependent on the steric and electronic properties of coupling partners; thus, carbohydrate synthesis is not easily predictable. Here we report the discovery of a macrocyclic bis-thiourea derivative that catalyzes stereospecific invertive substitution pathways of glycosyl chlorides.

The Development of Multidimensional Analysis Tools for Asymmetric Catalysis and Beyond.

In most modern organic chemistry reports, including many of ours, reaction optimization schemes are typically presented to showcase how reaction conditions have been tailored to augment the reaction's yield and selectivity. In asymmetric catalysis, this often involves evaluation of catalyst, solvent, reagent, and, sometimes, substrate features. Such an article will then detail the process's scope, which mainly focuses on its successes and briefly outlines the "limitations".

Using physical organic parameters to correlate asymmetric catalyst performance.

A classic strategy of physical organic chemists is to probe reaction mechanisms using linear free energy relationships. Identifying such relationships in asymmetric catalytic reactions provides substantial insight into the key factors controlling enantioselectivity, which in turn increases the predictability and applicability of these reactions. The focus of this JOCSynopsis is to highlight several recent examples in which various parameters were identified and applied to the elucidation of LFERs.

Prediction of catalyst and substrate performance in the enantioselective propargylation of aliphatic ketones by a multidimensional model of steric effects.

The effectiveness of a new asymmetric catalytic methodology is often weighed by the number of diverse substrates that undergo reaction with high enantioselectivity. Here we report a study that correlates substrate and ligand steric effects to enantioselectivity for the propargylation of aliphatic ketones. The mathematical model is shown to be highly predictive when applied to substrate/catalyst combinations outside the training set.

Multidimensional steric parameters in the analysis of asymmetric catalytic reactions.

Although asymmetric catalysis is universally dependent on spatial interactions to impart specific chirality on a given substrate, examination of steric effects in these catalytic systems remains empirical. Previous efforts by our group and others have seen correlation between steric parameters developed by Charton and simple substituents in both substrate and ligand; however, more complex substituents were not found to be correlative. Here, we review and compare the steric parameters common in quantitative structure activity relationships (QSAR), a common method for pharmaceutical function optimization, and how they might be applied in asymmetric catalysis, as the two fields are undeniably similar.

Three-dimensional correlation of steric and electronic free energy relationships guides asymmetric propargylation.

Chemical reaction outcomes are often rationalized on the basis of independent analyses of steric and electronic effects. We applied three-dimensional free energy relationships correlating steric and electronic effects to design and optimize a ligand class for the enantioselective Nozaki-Hiyama-Kishi propargylation of ketones. The resultant mathematical model describing the steric and electronic parameter relationship is highly reliant on the synergistic interactions of these two effects.

Predicting and optimizing asymmetric catalyst performance using the principles of experimental design and steric parameters.

Using a modular amino acid based chiral ligand motif, a library of ligands was synthesized systematically varying the substituents at two positions. The effects of these changes on ligand structure were probed in the enantioselective allylation of benzaldehyde, acetophenone, and methylethyl ketone under Nozaki-Hiyama-Kishi conditions. The resulting three-dimensional datasets allowed for the construction of mathematical surface models which describe the interplay of substituent effects on enantioselectivity for a given reaction.

Phase-transfer-catalyzed asymmetric acylimidazole alkylation.

2-Acylimidazoles are alkylated under phase-transfer conditions with cinchonidinium catalysts at -40 degrees C with allyl and benzyl electrophiles in high yield with excellent enantioselectivity (79 to >99% ee). The acylimidazole substrates are made in three steps from bromoacetic acid via the N-acylmorpholine adduct. The catalyst is made in high purity allowing for S-product formation (6-20 h) under mild conditions, consistent with an ion-pair mechanism.