Mechanistic studies of the sigmatropic rearrangement of o-allyl nitronic esters to y,o-unsaturated nitro naphthalene derivatives and nitro substituted cyclohexene derivatives

2021 ◽  
Author(s):  
Alma Pipic
Keyword(s):  
Sigmatropic Rearrangement ◽  
Mechanistic Studies ◽  
Naphthalene Derivatives ◽  
Cyclohexene Derivatives

scholarly journals Intermolecular 3+3 Ring Expansion of Aziridines to Dehydropiperidines through the Intermediacy of Aziridinium Ylides

2019 ◽  
Author(s):  
Jennifer Schomaker ◽  
Josephine Eshon ◽  
Kate A. Nicastri ◽  
Steven C. Schmid ◽  
William T. Raskopf ◽  
...  
Keyword(s):  
Natural Product ◽  
Functional Group ◽  
Ring Expansion ◽  
Sigmatropic Rearrangement ◽  
Reactive Intermediate ◽  
Mechanistic Studies ◽  
Reaction Conditions ◽  
Complex Molecules ◽  
Form Complex ◽  
Reaction Proceeds

Bicyclic aziridines undergo formal [3+3] ring expansion reactions when exposed to rhodium-bound vinyl carbenes to form complex dehydropiperidines in a highly stereocontrolled rearrangement. Mechanistic studies and DFT computations indicate the reaction proceeds through the formation of a vinyl aziridinium ylide; this reactive intermediate undergoes a concerted, asynchronous, pseudo-[1,4]- sigmatropic rearrangement to directly furnish the heterocyclic products with net retention at the new C-C bond. In combination with an asymmetric silver-catalyzed aziridination developed in our group, this method quickly delivers enantioenriched scaffolds with up to three contiguous stereocenters. The mild reaction conditions, functional group tolerance, and high stereochemical retention of this method are especially well-suited for appending piperidine motifs to natural product and complex molecules. Ultimately, our work establishes the value of underutilized aziridinium ylides as key intermediates in strategies to convert small, strained rings to larger N-heterocycles.

A Formal Metal-Free γ-Arylation of 1,3-Dicarbonyl Compounds via a Sequence of Isomerization/1,4-Addition/[3,3]-Sigmatropic Rearrangement

2021 ◽  
Author(s):  
Shi-Chao Lu ◽  
Fuqiang Wen ◽  
Xidong Guan
Keyword(s):  
Sigmatropic Rearrangement ◽  
Mechanistic Studies ◽  
Dicarbonyl Compounds ◽  
Metal Free

A metal-free redox arylation of alkynes with sulfoxides has been developed to provide an unconventional access to diverse γ-arylated 1,3-dicarbonyl compounds in an atom-economical manner. Mechanistic studies suggest that a...

scholarly journals Catalytic Chemoselective Sulfimidation with an Electrophilic [CoIII(TAML)]-Nitrene Radical Complex

2020 ◽  
Author(s):  
N.P. van Leest ◽  
J.I. van der Vlugt ◽  
Bas de Bruin
Keyword(s):  
Bond Formation ◽  
Sigmatropic Rearrangement ◽  
Mechanistic Studies ◽  
Aerobic Conditions ◽  
Product Yields ◽  
Radical Intermediates ◽  
Radical Complex ◽  
Nitrene Transfer ◽  
Allyl Sulfide ◽  
Cobalt Species

The cobalt species <b>PPh<sub>4</sub>[Co<sup>III</sup>(TAML<sup>red</sup>)]</b> is a competent and stable catalyst for the sulfimidation of (aryl)(alkyl)-substituted sulfides with iminoiodinanes reaching turnover numbers up to 900 and turnover frequencies of 640 min<sup>-1</sup> under mild and aerobic conditions. The sulfimidation proceeds in a highly chemoselective manner, even in the presence of alkenes or weak C-H bonds, as supported by inter- and intramolecular competition experiments. Functionalization of the sulfide substituent with various electron-donating and electron-withdrawing arenes and several alkyl, benzyl and vinyl fragments is tolerated, with up to quantitative product yields. Sulfimidation of phenyl allyl sulfide led to [2,3]-sigmatropic rearrangement of the initially formed sulfimide species to afford the corresponding <i>N</i>-allyl-<i>S</i>-phenyl-thiohydroxylamines as attractive products. Mechanistic studies suggest that the actual nitrene transfer to the sulfide proceeds via (previously characterized) electrophilic nitrene-radical intermediates that afford the sulfimide products via electronically asynchronous transition states, in which SET from the sulfide to the nitrene-radical complex precedes N-S bond formation in a single concerted process. <br>

scholarly journals Intermolecular 3+3 Ring Expansion of Aziridines to Dehydropiperidines through the Intermediacy of Aziridinium Ylides

2019 ◽  
Author(s):  
Jennifer Schomaker ◽  
Josephine Eshon ◽  
Kate A. Nicastri ◽  
Steven C. Schmid ◽  
William T. Raskopf ◽  
...  
Keyword(s):  
Natural Product ◽  
Functional Group ◽  
Ring Expansion ◽  
Sigmatropic Rearrangement ◽  
Reactive Intermediate ◽  
Mechanistic Studies ◽  
Reaction Conditions ◽  
Complex Molecules ◽  
Form Complex ◽  
Reaction Proceeds

Bicyclic aziridines undergo formal [3+3] ring expansion reactions when exposed to rhodium-bound vinyl carbenes to form complex dehydropiperidines in a highly stereocontrolled rearrangement. Mechanistic studies and DFT computations indicate the reaction proceeds through the formation of a vinyl aziridinium ylide; this reactive intermediate undergoes a concerted, asynchronous, pseudo-[1,4]- sigmatropic rearrangement to directly furnish the heterocyclic products with net retention at the new C-C bond. In combination with an asymmetric silver-catalyzed aziridination developed in our group, this method quickly delivers enantioenriched scaffolds with up to three contiguous stereocenters. The mild reaction conditions, functional group tolerance, and high stereochemical retention of this method are especially well-suited for appending piperidine motifs to natural product and complex molecules. Ultimately, our work establishes the value of underutilized aziridinium ylides as key intermediates in strategies to convert small, strained rings to larger N-heterocycles.

scholarly journals Catalytic Chemoselective Sulfimidation with an Electrophilic [CoIII(TAML)]-Nitrene Radical Complex

2020 ◽  
Author(s):  
N.P. van Leest ◽  
J.I. van der Vlugt ◽  
Bas de Bruin
Keyword(s):  
Bond Formation ◽  
Sigmatropic Rearrangement ◽  
Mechanistic Studies ◽  
Aerobic Conditions ◽  
Product Yields ◽  
Radical Intermediates ◽  
Radical Complex ◽  
Nitrene Transfer ◽  
Allyl Sulfide ◽  
Cobalt Species

The cobalt species <b>PPh<sub>4</sub>[Co<sup>III</sup>(TAML<sup>red</sup>)]</b> is a competent and stable catalyst for the sulfimidation of (aryl)(alkyl)-substituted sulfides with iminoiodinanes reaching turnover numbers up to 900 and turnover frequencies of 640 min<sup>-1</sup> under mild and aerobic conditions. The sulfimidation proceeds in a highly chemoselective manner, even in the presence of alkenes or weak C-H bonds, as supported by inter- and intramolecular competition experiments. Functionalization of the sulfide substituent with various electron-donating and electron-withdrawing arenes and several alkyl, benzyl and vinyl fragments is tolerated, with up to quantitative product yields. Sulfimidation of phenyl allyl sulfide led to [2,3]-sigmatropic rearrangement of the initially formed sulfimide species to afford the corresponding <i>N</i>-allyl-<i>S</i>-phenyl-thiohydroxylamines as attractive products. Mechanistic studies suggest that the actual nitrene transfer to the sulfide proceeds via (previously characterized) electrophilic nitrene-radical intermediates that afford the sulfimide products via electronically asynchronous transition states, in which SET from the sulfide to the nitrene-radical complex precedes N-S bond formation in a single concerted process. <br>

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