6-exo-trig Michael addition-lactonizations for catalytic enantioselective chromenone synthesis

Neyyappadath, Rifahath M.; Cordes, David B.; Slawin, Alexandra M. Z.; Smith, Andrew D.

doi:10.1039/c6cc10178j

Cited by 27 publications

(7 citation statements)

References 45 publications

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“…The starting material was enone acetic acid tethered by aromatic ring 60 which was treated with pivaolyl chloride in presence of base and ( S )‐tetramisole·HCl 4a as catalyst to facilitate an intramolecular ring closure delivering cis ‐chromenone derivatives 63 in good yields and excellent stereoselctivities (Scheme 25). [ 32 ]…”

Section: Six Membered Heterocycle Formation By Formal and Concerted [mentioning

confidence: 99%

Synthesis of Heterocycles by isothiourea organocatalysis

Biswas¹,

Mondal

Maji

2020

Journal of Heterocyclic Chem

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Isothiourea was first employed as catalyst by Birman in 2006 for the enantioselective acyl transfer reaction. The catalyst was then well explored in the course of kinetic resolution and desymmetrization studies. A few years later, Romo and Smith applied isothiourea catalysis in enantioselective cascade reactions to prepare carbocycles and heterocycles acessing new reactivities of isothiourea. Several research groups were then attracted toward this new field of organocatalysis, and applied isothioureas as nucleophilic catalysts in executing cascade methodologies to synthesize various intresteting molecular scaffolds including heterocycles. The present review documents a summary on the construction of heterocyclic molecules by isothiourea organocatalysis. Heterocycles are of prime interest to organic chemists due to their omnipresence in natural products and bioactive molecules. The Lewis basic nucleophilic catalyst isothioureas play a pivotal role in the cascades to generate either α,β‐unsaturated acyl isothiouronium ion or isothiouronium enolate as the prime reaction intermediate. We have covered the reactions involving two intermediates of opposite reactivities affording various heterocycles.

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Section: Six Membered Heterocycle Formation By Formal and Concerted [mentioning

confidence: 99%

Synthesis of Heterocycles by isothiourea organocatalysis

Biswas¹,

Mondal

Maji

2020

Journal of Heterocyclic Chem

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“…The starting intermediate b was prepared according to the described procedure [16] from commercially available ketone a .…”

Section: Methodsmentioning

confidence: 99%

Tautomerism as primary signaling mechanism in metal sensing: the case of amide group

Deneva

Dobrikov

Crochet

et al. 2019

Beilstein J. Org. Chem.

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The concept for sensing systems using the tautomerism as elementary signaling process has been further developed by synthesizing a ligand containing 4-(phenyldiazenyl)naphthalene-1-ol as a tautomeric block and an amide group as metal capturing antenna. Although it has been expected that the intramolecular hydrogen bonding (between the tautomeric hydroxy group and the nitrogen atom from the amide group) could stabilize the pure enol form in some solvents, the keto tautomer is also observed. This is a result from the formation of intramolecular associates in some solvents. Strong bathochromic and hyperchromic effects in the visible spectra accompany the 1:1 formation of complexes with some alkaline earth metal ions.

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“…The reaction proceeded through a 6- exo -trig-Michael addition/ O -acylation sequence to deliver cis -chromenone derivatives 98 (Scheme 17c ). 22f In this context, amidines, which have structural features that resemble isothioureas, have been used as catalysts to obtain chiral enolates from in situ generated mixed anhydrides. These enolates are then utilized to trap ortho -quinone methides via asymmetric [4+2] cycloaddition (not shown in the scheme).…”

Section: Catalysis Through Covalent Activationmentioning

confidence: 99%

Organocatalyzed Oxa-Diels–Alder Reactions: Recent Progress

et al. 2021

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Oxa-Diels-Alder reaction is a straightforward, atom-economical process for the construction of six membered oxa-cycle which is a privileged structure due to its omnipresence in several pharmaceuticals and natural products. Like many other asymmetric transformations, organocatalysis provides an elegant pathway to their synthesis via [4+2] annulation under mild reaction conditions. The oxa-Diels reactions either utilize α,β-unsaturated carbonyl as oxadiene with a suitable dienophile or simple carbonyl as dienophile with other dienes. A range of organocatalysts have been explored in the past decade to execute this strategy. The catalysts induce stereoselectivities via two basic reactivities: 1) Formation of chiral intermediates, 2) Selectively activating suitable reactants in transition state. The present review assembles organocatalyzed asymmetric oxa-Diels-Alder reactions published in last ten years’ time span with detailed discussion on mechanistic approaches.

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6-exo-trig Michael addition-lactonizations for catalytic enantioselective chromenone synthesis

Abstract: The catalytic enantioselective 6-exo-trig Michael addition-lactonization of enone-acid substrates to form cis-chromenones with high diastereo- and enantiocontrol was developed using the commercially available isothiourea tetramisole.

Cited by 27 publications

References 45 publications

Synthesis of Heterocycles by isothiourea organocatalysis

Synthesis of Heterocycles by isothiourea organocatalysis

Tautomerism as primary signaling mechanism in metal sensing: the case of amide group

Organocatalyzed Oxa-Diels–Alder Reactions: Recent Progress

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