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Polyene cyclizations are among the most complex and challenging transformations in biology. In a single reaction step, multiple carbon–carbon bonds, ring systems and stereogenic centres are constituted from simple, acyclic precursors1–3. Simultaneously achieving this kind of precise control over product distribution and stereochemistry poses a formidable task for chemists. In particular, the polyene cyclization of (3E,7E)-homofarnesol to the valuable naturally occurring ambergris odorant (−)-ambrox is recognized as a longstanding challenge in chemical synthesis1,4–7. Here we report a diastereoselective and enantioselective synthesis of (−)-ambrox and the sesquiterpene lactone natural product (+)-sclareolide by a catalytic asymmetric polyene cyclization by using a highly Brønsted-acidic and confined imidodiphosphorimidate catalyst in the presence of fluorinated alcohols. Several experiments, including deuterium-labelling studies, suggest that the reaction predominantly proceeds through a concerted pathway in line with the Stork–Eschenmoser hypothesis8–10. Mechanistic studies show the importance of the enzyme-like microenvironment of the imidodiphosphorimidate catalyst for attaining exceptionally high selectivities, previously thought to be achievable only in enzyme-catalysed polyene cyclizations.The catalytic asymmetric polyene cyclization of homofarnesol to ambrox is achieved using a highly Brønsted-acidic and confined imidodiphosphorimidate catalyst. [ABSTRACT FROM AUTHOR]

A strong and confined Brønsted acid catalyzed enantioselective cyclization of bis(methallyl)silanes provides enantioenriched Si-stereogenic silacycles. High enantioselectivities of up to 96.5:3.5 er were obtained for a range of bis(methallyl)silanes. NMR and ESI-MS studies reveal that the formation of a covalent adduct irreversibly inhibits turnover. Remarkably, we found that acetic acid as an additive promotes the collapse of this adduct, enabling full turnover. Experimental investigation and density functional theory (DFT) calculations were conducted to elucidate the origin of this phenomenon and the observed enantioselectivity. Among the diverse organosilicon compounds, Si-stereogenic silanes have recently demonstrated promising biological activities but only few protocols for the preparation of organosilicon compounds possessing a Si-stereogenic center exist in the literature. Here the authors show that a strong and confined Brønsted acid catalyzed enantioselective cyclization of bis(methallyl)silanes and provides enantioenriched Si-stereogenic silacycles. [ABSTRACT FROM AUTHOR]

Asymmetric catalysis is an advanced area of chemical synthesis, but the handling of abundantly available, purely aliphatic hydrocarbons has proven to be challenging. Typically, heteroatoms or aromatic substructures are required in the substrates and reagents to facilitate an efficient interaction with the chiral catalyst. Confined acids have recently been introduced as tools for homogenous asymmetric catalysis, specifically to enable the processing of small unbiased substrates1. However, asymmetric reactions in which both substrate and product are purely aliphatic hydrocarbons have not previously been catalysed by such super strong and confined acids. We describe here an imidodiphosphorimidate-catalysed asymmetric Wagner–Meerwein shift of aliphatic alkenyl cycloalkanes to cycloalkenes with excellent regio- and enantioselectivity. Despite their long history and high relevance for chemical synthesis and biosynthesis, Wagner–Meerwein reactions utilizing purely aliphatic hydrocarbons, such as those originally reported by Wagner and Meerwein, had previously eluded asymmetric catalysis.We describe an imidodiphosphorimidate-catalysed asymmetric Wagner–Meerwein shift of aliphatic alkenyl cycloalkanes to cycloalkenes with excellent regio- and enantioselectivity. [ABSTRACT FROM AUTHOR]

This article discusses the development of a Brønsted acid catalyzed asymmetric silylation method for biaryl diols, which allows for the synthesis of axially chiral biaryl silyl ethers. The researchers tested different catalysts and reaction conditions to optimize the enantioselectivity of the silylation reaction. They also conducted control experiments to confirm that the reaction proceeds through a desymmetrization-kinetic resolution sequence. The authors acknowledge the contribution of Professor Martin Oestreich, who independently investigated the same transformation. [Extracted from the article]

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Copyright of Angewandte Chemie is the property of Wiley-Blackwell and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

We disclose a highly regioselective, catalytic one‐step dehydrogenation of α‐substituted cyclic ketones in the presence of 2,3‐dichlorobenzo‐5,6‐dicyano‐1,4‐benzoquinone (DDQ). The high regioselectivity originates from a phosphoric acid‐catalyzed enolization, selectively affording the thermodynamically preferred enol, followed by the subsequent oxidation event. Our method provides reliable access to several α‐aryl and α‐alkyl substituted α,β‐unsaturated ketones. [ABSTRACT FROM AUTHOR]

Toward a conversion of aldehydes into arenes, we designed a sequence involving the initial reaction of an aldehyde to give a fulvene, followed by photochemical and platinum‐catalyzed rearrangements into a Dewar benzene derivative, which finally isomerizes into the targeted arene. While computational studies support the plausibility of this route, we found that fulvene irradiation resulted in an unexpected isomerization into a spiro[2.4]heptadiene. This unusual photorearrangement has been investigated mechanistically and provides access to a variety of spiro[2.4]heptadienes with different substituents. [ABSTRACT FROM AUTHOR]

We report the synthesis of a novel spirocyclic quaternary ammonium salt that possesses axial chirality. Enantiopure material was obtained by fractional crystallization of the corresponding (R,R)‐tartrate salt. Application of this chiral quaternary ammonium salt in phase‐transfer catalytic asymmetric alkylation of glycinate Schiff base was examined. [ABSTRACT FROM AUTHOR]

The selective conversion of natural or synthetic neral to (1R,6S)-trans-isopiperitenol would enable and expedite sustainable routes to menthol1,2 and cannabinoids3–5. However, this reaction has been considered impossible because its product is more reactive to the required acid catalysts than its starting material, resulting in several side products6–9. We now show that an unsymmetric, strong and confined chiral acid, a highly fluorinated imino-imidodiphosphate, catalyses this process with excellent efficiency and selectivity. Expanding the method to other α,β-unsaturated aldehydes could enable access to new cannabinoids and menthol derivatives not readily accessible previously. Mechanistic studies suggest that the confined catalyst accomplishes this reaction by binding the product in an unreactive conformation, thereby preventing its decomposition. We also show how (1R,6S)-trans-isopiperitenol can be readily converted to pharmaceutically useful cannabinoids and menthol, each in the shortest and most atom-economic routes so far.An unsymmetric, strong and confined chiral acid, a highly fluorinated imino-imidodiphosphate, catalyses the selective conversion of neral to (1R,6S)-trans-isopiperitenol, enabling sustainable routes to menthol and cannabinoids. [ABSTRACT FROM AUTHOR]

Catalyst optimization processes typically rely on inductive and qualitative assumptions of chemists based on screening data. While machine learning models using molecular properties or calculated 3D structures enable quantitative data evaluation, costly quantum chemical calculations are often required. In contrast, readily available binary fingerprint descriptors are time‐ and cost‐efficient, but their predictive performance remains insufficient. Here, we describe a machine learning model based on fragment descriptors, which are fine‐tuned for asymmetric catalysis and represent cyclic or polyaromatic hydrocarbons, enabling robust and efficient virtual screening. Using training data with only moderate selectivities, we designed theoretically and validated experimentally new catalysts showing higher selectivities in a challenging asymmetric tetrahydropyran synthesis. [ABSTRACT FROM AUTHOR]

Catalyst optimization processes typically rely on inductive and qualitative assumptions of chemists based on screening data. While machine learning models using molecular properties or calculated 3D structures enable quantitative data evaluation, costly quantum chemical calculations are often required. In contrast, readily available binary fingerprint descriptors are time‐ and cost‐efficient, but their predictive performance remains insufficient. Here, we describe a machine learning model based on fragment descriptors, which are fine‐tuned for asymmetric catalysis and represent cyclic or polyaromatic hydrocarbons, enabling robust and efficient virtual screening. Using training data with only moderate selectivities, we designed theoretically and validated experimentally new catalysts showing higher selectivities in a challenging asymmetric tetrahydropyran synthesis. [ABSTRACT FROM AUTHOR]