Asymmetric Organocatalysis: A Survival Guide to Medicinal Chemists

Majority of drugs act by interacting with chiral counterparts, e.g., proteins, and we are, unfortunately, well-aware of how chirality can negatively impact the outcome of a therapeutic regime. The number of chiral, non-racemic drugs on the market is increasing, and it is becoming ever more important to prepare these compounds in a safe, economic, and environmentally sustainable fashion. Asymmetric organocatalysis has a long history, but it began its renaissance era only during the first years of the millennium. Since then, this field has reached an extraordinary level, as confirmed by the awarding of the 2021 Chemistry Nobel Prize. In the present review, we wish to highlight the application of organocatalysis in the synthesis of enantio-enriched molecules that may be of interest to the pharmaceutical industry and the medicinal chemistry community. We aim to discuss the different activation modes observed for organocatalysts, examining, for each of them, the generally accepted mechanisms and the most important and developed reactions, that may be useful to medicinal chemists. For each of these types of organocatalytic activations, select examples from academic and industrial applications will be disclosed during the synthesis of drugs and natural products

Asymmetric Organocatalysis: A Survival Guide to Medicinal Chemists

Majority of drugs act by interacting with chiral counterparts, e.g., proteins, and we are, unfortunately, well-aware of how chirality can negatively impact the outcome of a therapeutic regime. The number of chiral, non-racemic drugs on the market is increasing, and it is becoming ever more important to prepare these compounds in a safe, economic, and environmentally sustainable fashion. Asymmetric organocatalysis has a long history, but it began its renaissance era only during the first years of the millennium. Since then, this field has reached an extraordinary level, as confirmed by the awarding of the 2021 Chemistry Nobel Prize. In the present review, we wish to highlight the application of organocatalysis in the synthesis of enantio-enriched molecules that may be of interest to the pharmaceutical industry and the medicinal chemistry community. We aim to discuss the different activation modes observed for organocatalysts, examining, for each of them, the generally accepted mechanisms and the most important and developed reactions, that may be useful to medicinal chemists. For each of these types of organocatalytic activations, select examples from academic and industrial applications will be disclosed during the synthesis of drugs and natural products.The authors acknowledge the Spanish Agencia Estatal de Investigación (FEDER-PID2020-118422-GB-I00), the Basque Government (Grupos IT1558-22), and the University of Bologna for financial support

Enantioselective transannular reactions by palladium-catalysed conjugate addition of aryl boronic acids

A palladium-catalyzed asymmeric conjugate addition of aryl boronic acids to medium-sized cycloalkenones followed by intramolecular aldol trapping is reported. The use of in situ formed [Pd/(QuinoxP*)] as the catalyst enables the synthesis of arylbicyclic scaffolds in good yields and with excellent stereocontrol (up to 7 : 1 dr, up to 99% ee). The reaction is applicable to a range of medium size ketoenone substrates and funcionalized aryl boronic acids, including heterocyclic compounds.Spanish Ministerio de Ciencia, Innovación y Universidades (MCIU), grant numbers FEDER-PID2019-106358GB-C21, FEDER-PID2020-118422-GB-I00, contract RYC-2017-22294 for V. H., Basque Government, grant number Grupos IT908-16, Junta de Andalucía (US-1260906)

Transannular Enantioselective (3 + 2) Cycloaddition of Cycloalkenone Hydrazones under Bronsted Acid Catalysis.

[EN]Hydrazones derived from cycloalkenones undergo an enantioselective transannular formal (3 + 2) cycloaddition catalyzed by a chiral phosphoric acid. The reaction provides high yields and excellent stereocontrol in the formation of complex adducts with one or two α-tertiary amine moieties at the ring fusion, and these can be converted into very versatile stereodefined decalin- or octahydro-1H-indene-derived 1,3-diamines through simple reductive N–N cleavage.This research was supported by the Spanish Ministerio de Ciencia, Innovación y Universidades (MCIU) through projects FEDER-PID2020-118422-GB-I00, FEDER-PID2019-109674-GB-I00 and FPI fellowship to J.S. and by the Basque Government (IT908-16). J.S. acknowledges the Spanish MCIU for an FPI fellowship

Recent Advances in the Prins Reaction

The Prins reaction is a very convenient synthetic platform for the preparation of oxygen-containing heterocyclic compounds, especially tetrahydropyrans and tetrahydrofurans. While this reaction has been extensively used by synthetic chemists since its discovery, the last years have witnessed impressive improvements in its performance and scope and especially in the development of new catalytic and enantioselective versions. This mini-review presents these recent advances through selected representative examples.The authors thank the Spanish Agencia Estatal de Investigacion (FEDER-PID2020-118422-GB-I00) and the Basque Government (Grupos IT1558-22) for financial support

Switchable Brønsted acid-catalyzed ring contraction of Cyclooctatetraene oxide towards the enantioselective synthesis of Cyloheptatrienyl-substituted homoallylic Alcohols and Oxaborinanes

The ability of cyclooctatetraene oxide to undergo two sequential ring contraction events under mild conditions, using Brønsted acid catalysis, has been studied in detail. We have found that the selectivity can be controlled by the acidity of the catalyst and by the temperature, being able to obtain selectively either the cycloheptatriene carbaldehyde product, arising from a single ring-contraction event, or phenylacetaldehyde that is formed after a second ring contraction process. A complete mechanistic picture of the reaction and a rationale behind the influence of the catalyst is provided based on both experimental and computational data. Finally, this acid-catalyzed ring contraction has been coupled with an in situ enantioselective allylation reaction, delivering enantioenriched cycloheptatrienyl-substituted homoallylic alcohols when it is carried out in the presence of a chiral phosphoric acid catalyst. These homoallylic alcohols have also been converted into enantioenriched oxaborinanes through copper-catalyzed nucleophilic borylation/cyclization protocol

Recent Developments in Transannular Reactions

Transannular reactions have shown a remarkable performance for the construction of polycyclic scaffolds from medium- or large-sized cyclic molecules in an unconventional manner. Recent examples of transannular reactions reported from 2011 have been reviewed, emphasizing the excellent performance of this approach when accessing the target compounds. This review also highlights how this methodology provides an alternative approach to other commonly used strategies for the construction of cyclic entities such as cyclization or cycloaddition reactions.MCIU (FEDER-PID2020-118422-gb-100), Basque Government (IT908-16

Asymmetric Dual Enamine Catalysis/Hydrogen Bonding Activation

Asymmetric enamine base activation of carbonyl compounds is a well-known and widely used strategy for providing functionalization of organic compounds in an efficient way. The use of solely organic substances, which in most cases are commercially available primary or secondary amines that are easy to obtain, avoids the use of hazardous substances or metal traces, making this type of catalysis a highly convenient methodology from a sustainable point of view. In many cases, the reactivity or the stereoselectivity obtained is far from being a practical and advantageous strategy; this can be improved by using a hydrogen bonding co-catalyst that can help during the activation of one species or by using a bifunctional catalyst that can direct the approximation of reagents during the reaction outcome. In this review, we describe the most efficient methodologies that make use of a dual activation of reagents for performing α-functionalization (enamine activation) or remote functionalization (such as dienamine or trienamine activation) of carbonyl compounds.PID2020-118422GB-I00 funded by MCIN/AEI/10.13039/501100011033 and by “ESF Investing in your future” are gratefully acknowledged together with the Basque Government (Grupos IT1558-22) and the University of the Basque Country (UPV/EHU)

Ion-pairing catalysis in the enantioselective addition of hydrazones to N-acyldihydropyrrole derivatives

We have demonstrated that dihydropyrrole-based enamide derivatives can act as efficient precursors of chiral quaternary N-acyliminium salts under Brønsted acid catalysis that undergo reactions with hydrazones, the latter participating as masked nucleophilic carbonyl group equivalents. The optimized methodology provides a variety of enantiopure α-substituted proline derivatives in excellent yields, being even compatible with disubstituted β-enamides that generate two contiguous stereocentres.Spanish MINECO(FEDER-CTQ201783633-P), the Basque Government (IT908-16) and UPV/EHU (EHUA15/24 and a fellowship to N.Z.

Desymmetrization of Oxabenzonorbornadienes through Brønsted Acid-Catalyzed Enantioselective (3+2) Cycloaddition with Hydrazones

This work presents the desymmetrization of oxabenzonorbornadienes through the (3+2) cycloaddition reaction with hydrazones using a chiral Brønsted acid such as a BINOL-derived phosphoramide. This chiral acid catalyst appears as the most effective mediator for the activation of the hydrazone via hydrazonium cation that reacts in a (3+2) fashion with the oxabenzonorbornadiene as the olefinic counterpart. Under the optimized conditions, the reaction provided selectively exo cycloaddition products in satisfactory yields and moderate stereoselectivities. The scope of the reaction was explored displaying 21 examples of these highly functionalized tetrahydroepoxybenzoindazole compounds. A reaction mechanism is proposed to explain the outcome of the reaction.Grant PID2020-118422GB-I00 funded by MCIN/AEI/10.13039/501100011033 and by “ESF Investing in your future” is gratefully acknowledged. Financial support by the the Basque Government (Grupos IT1558-22) is also gratefully acknowledged