Enantiomerically pure vinyl ketene acetals as dienes in the Diels-Alder reaction

Konopelski, Joseph P.; Boehler, Mark A.

doi:10.1021/ja00194a066

Cited by 38 publications

(8 citation statements)

References 1 publication

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“…Ketene acetals are an important class of organic reactants and intermediates . Specifically, ketene O , O - or N , O -acetals have proven useful as synthons in α, β-unsaturated ester production, lactone synthesis, uncatalyzed polymerization, nontraditional aldol condensation, anodic olefin coupling, Claisen rearrangements, and Diels–Alder reactions . Although ketene acetals are widely used in many synthetic processes, methods of their synthesis are dominated by silylation of ester enolates (Figure , A). − , Moreover, reports of isolable, silyl ketene acetals do exist and are easily accessible. − ,, However, the synthesis of alkyl ketene O , O - or N , O -acetals is more challenging.…”

Section: Introductionmentioning

confidence: 99%

Electrophilic Etherification of α-Heteroaryl Carbanions with Monoperoxyacetals as a Route to Ketene O,O- and N,O-Acetals

2021

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Alkyl ketene acetals are useful reactants in a variety of synthetic processes, and yet, there are limited routes to their formation as isolable products. We now report the successful synthesis and isolation of heteroaryl ketene acetals through intermolecular transfer of alkoxyl (δ + OR) from electrophilic peroxides to lithiated benzofurans, indoles, and pyridines. Primary and secondary peroxyacetals enable selective transfer of the nonanomeric alkoxy group in moderate to high yield; substrates bearing an electron-donating substituent show enhanced reactivity toward electrophilic oxygen. Heteroaryl ketene acetals are remarkably stable throughout traditional purification techniques; the superior stability of ketene N,O-acetals compared to ketene O,O-acetals is presumably due to increased aromaticity of the indole and pyridine structures. The presented method overcomes typical problems associated with alkyl ketene acetal synthesis as reported products withstood workup and flash column chromatography procedures.

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Section: Introductionmentioning

confidence: 99%

Electrophilic Etherification of α-Heteroaryl Carbanions with Monoperoxyacetals as a Route to Ketene O,O- and N,O-Acetals

2021

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“… 106 The desired stereochemical biases was induced by intramolecular PKR resulting in the placement of the peripheral exo substituents. 107 Finally, the latter was converted to the desired natural product hamigeran B 97 in two steps ( Scheme 11 ). 104 …”

Section: Applications Of Pauson–khand Reaction In the Total Synthesis...mentioning

confidence: 99%

Application of Pauson–Khand reaction in the total synthesis of terpenes

Heravi

Mohammadi

2021

RSC Adv.

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“…85,86,91 Lastly, due to their electron-rich nature, ketene N,O-acetals make facile dienes or dienophiles in a diverse set of rearrangement (Tables 13-17) or Diels-Alder reactions (Scheme 8, Table 18). 94,99 Given these reports, ketene N,O-acetals seem to be practical, and advantageous, substitutes for other acetal homologues. Specifically, from contemporary efforts to increase the stability of N,O-acetals, the title functional group has clearly exceeded the common stability of their renowned, O,O-counterparts; 13a moreover, several means of obtaining isolable, yet functionalized, ketene N,Oacetals now exist and are easily accessible.…”

Section: Conclusion Perspectives and Directionsmentioning

confidence: 99%

“…As a reactive, electron-rich functional group, ketene acetals are classic reagents in the Diels-Alder reaction. 99 Furthermore, Diels-Alder transformations are an elegant means of obtaining heterocyclic or quaternary carbon motifs found in natural products; being so, given the enhanced reactivity of ketene N,O-acetals, compared to their N,N-or S,S-homologues, select, contemporary reports have utilized the former in facile, Diels-Alder reactions. For example, in 2000, the group supplemented their reports on the Eschenmoser-Claisen rearrangement of ketene N,O-acetals with Diels-Alder reactions of the same substrates (Scheme 8).…”

Section: Ketene No-acetals As Dienes or Dienophiles In Diels-alder Re...mentioning

confidence: 99%

Modern Synthesis and Chemistry of Stabilized Ketene N,O-Acetals

Paris

Willand‐Charnley

2021

Synthesis

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Ketene N,O-acetals are robust and versatile synthons. Herein, we outline the synthesis of stable ketene N,O-acetals in the twenty-first century. In addition, we review recent developments in the chemistry of ketene N,O-acetals, as it applies to the vinylogous Mukaiyama aldol reaction, electrolysis, and pericyclic transformations. While dated reports rely on in situ use, modern methods of ketene N,O-acetal synthesis are heavily oriented towards producing products with high “bench” stability; moreover, in the present century, chemists typically enhance the stability of ketene N,O-acetals by positioning an electron-withdrawing group at the β-terminus or at the N-position. As propitious substrates in the vinylogous Mukaiyama aldol reaction, ketene N,O-acetals readily provide polyketide adducts with high regioselectivity. When exposed to electrolysis conditions, the title functional group forms a reactive radical cation and cleanly couples with a variety of activated olefins. Given their electron-rich nature, ketene N,O-acetals act as facile substrates in several rearrangement reactions; further, ketene N,O-acetals reserve the ability to act as either dienophiles or dienes in Diels-Alder reactions. Lastly, ketene N,O-acetals are seemingly more stable than their O,O- counterparts and more reactive than analogous N,N- or S,S-acetals; these factors, in combination, make ketene N,O-acetals advantageous substitutes for other ketene acetal homologs.

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Enantiomerically pure vinyl ketene acetals as dienes in the Diels-Alder reaction

Cited by 38 publications

References 1 publication

Electrophilic Etherification of α-Heteroaryl Carbanions with Monoperoxyacetals as a Route to Ketene O,O- and N,O-Acetals

Electrophilic Etherification of α-Heteroaryl Carbanions with Monoperoxyacetals as a Route to Ketene O,O- and N,O-Acetals

Application of Pauson–Khand reaction in the total synthesis of terpenes

Modern Synthesis and Chemistry of Stabilized Ketene N,O-Acetals

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