Stereoselective Synthesis of Pyrans from Epoxyalkenes: Dual Catalysis with Palladium and Brønsted Acid

Setterholm, Noah A.; McDonald, Frank E.

doi:10.1021/acs.joc.8b00026

Cited by 11 publications

(1 citation statement)

References 40 publications

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“…The relatively low nucleophilicity of alkynes compared with alkene analogues is an obstacle to their use in cationic cascade reactions, especially in the intermolecular version. Nevertheless, examples of bimolecular capture of C‐electrophiles with alkynes are also known . A comparative study of the interrupted Nazarov reaction with the interception of triple and double bonds as nucleophiles has been carried out (Scheme ) .…”

Section: Interrupted Nazarov‐type Reactionmentioning

confidence: 99%

Recent Advances in the Interrupted Nazarov Reaction

Yadykov

Ширинян

2019

Adv Synth Catal

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In recent decades there have been significant improvements in the efficiency of synthesis as a result of considerable progress in tandem reactions, cascade transformations and related one‐pot processes. These methodologies are less time‐consuming, more cost‐effective, and produce less waste compared to the classical stepwise protocols. The Nazarov cyclization is an important and versatile method for the synthesis of five‐membered carbocycles which are found in many natural compounds and functional molecules. Current activities in the field of the Nazarov reaction are focused on development of better catalysts, asymmetric options and increasing the efficiency of synthesis. This transformation is suitable for applying to an intensified step‐economy in interrupted versions and one‐pot protocols. Interrupted Nazarov reactions in particular take advantage of the stereospecific nature of the electrocyclization. The universality of these reactions has facilitated an access to a plethora of complex small molecules of high medicinal relevance. In this review, we present a comprehensive summary of recent advances in the interrupted Nazarov‐type cyclization, and classify these reactions according to the structure of the substrate or the reaction mechanism. This is the first review that presents a survey on various types of interrupted Nazarov cyclization and deals with the recent advances, especially using tandem/domino or one‐pot reaction strategies and covers the literature from 2009 to 2019.

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Section: Interrupted Nazarov‐type Reactionmentioning

confidence: 99%

Recent Advances in the Interrupted Nazarov Reaction

Yadykov

Ширинян

2019

Adv Synth Catal

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An Enamide‐Based Domino Reaction for a Highly Stereoselective Synthesis of Tetrahydropyrans

et al. 2019

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A novel method for the highly stereoselective synthesis of tetrahydropyrans is reported. This domino reaction is based on a twofold addition of enamides to aldehydes followed by a subsequent cyclization and furnishes fully substituted tetrahydropyrans in high yields. Three new σ‐bonds and five continuous stereogenic centers are formed in this one‐pot process with a remarkable degree of diastereoselectivity. In most cases, the formation of only one out of 16 possible diastereomers is observed. Two different stereoisomers can be accessed in a controlled fashion starting either from an E‐ or a Z‐configured enamide.

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Bioinspired Asymmetric Total Synthesis of Emeriones A–C**

Jänner

Isak

et al. 2022

Angewandte Chemie

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We report asymmetric bioinspired total syntheses of the fungal metabolites emeriones A-C via stereoselective oxidations of two bicyclo[4.2.0]octadiene diastereomers. The central bicyclic scaffolds are prepared in an 8π/6π electrocyclization cascade of a stereodefined pentaene, which contains the fully assembled side chains of the emeriones. The anti-aldol side chain is made using a Paterson-aldol addition, and the epoxide of the dioxabicyclo[3.1.0]hexane side chain via ring-closure onto an oxidized acetal. Our work has enabled the structural revision of emerione C, and resulted in the synthesis of a "missing" family member, which we call emerione D. DFT calculations identified two methyl groups that govern torquoselectivity in the 8π/6π cascade.Natural products derived from polyenes that undergo cyclization/isomerization cascades initiated by an 8π electrocyclization have intrigued chemists for decades. [1] The emeriones (Figure 1), one such family of natural products that were isolated from the fungus E. nidulans, [2] display oxidized bicyclo[4.2.0]octadiene cores (red) flanked by a seven carbon aldol fragment (blue) and a propenyl-substituted dioxabicyclo[3.1.0]hexane system (black). The two side chains (blue and black) of emerione A (1) and B (2) share the same absolute configurations, while the bicyclo-[4.2.0]octadieneoxide central scaffolds are enantiomeric with respect to each other. Emerione C has a bridging endoperoxide on the central core, and its proposed structure has a stereochemical configuration similar to emerione B.Related substances like shimalactone A (3) [1p] and ocellapyrone B (4) [1m, n] have been synthesized, but the emeriones are arguably the most complex examples of such natural products, each containing twelve stereocenters, eight of which are contiguous, and two quaternary. Moreover, the dioxabicyclo[3.1.0]hexane system, also found in natural products like verrucosidin (5), [3] is a considerable synthetic challenge alongside the oxidized bicyclo[4.2.0]octadiene scaffolds. Emerione A inhibits NO production in lipopolysaccharide-induced RAW264.7 cells [2] as well as NDM-1 [4] at low micromolar concentrations, but the emeriones appear not to have been tested in other assays. Motivated both by their striking structures and potentially undiscovered bioactivities, we chose to target the emeriones for synthesis. We describe herein the successful completion of the syntheses, the structural revision of emerione C, and the synthesis of the originally proposed structure of emerione C, which we name emerione D.

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Stereoselective Synthesis of Pyrans from Epoxyalkenes: Dual Catalysis with Palladium and Brønsted Acid

Cited by 11 publications

References 40 publications

Recent Advances in the Interrupted Nazarov Reaction

Recent Advances in the Interrupted Nazarov Reaction

An Enamide‐Based Domino Reaction for a Highly Stereoselective Synthesis of Tetrahydropyrans

Bioinspired Asymmetric Total Synthesis of Emeriones A–C**

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