The superacid-promoted reactions of alpha-hydroxy and alpha-ketoamides have been studied. Ionization of these compounds leads to varied aryl-substituted oxyindole products. In some cases, electrocyclization can lead to substituted fluorene products. Dicationic, superelectrophilic intermediates are proposed as intermediates leading to the products from alpha-hydroxy and alpha-ketoamides.
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http://dx.doi.org/10.1021/jo801208m | DOI Listing |
J Org Chem
August 2023
Department of Chemistry and Biochemistry, Northern Illinois University, DeKalb, Illinois 60115, United States.
-Heterocyclic alcohols are shown to be excellent substrates for superacid-promoted Friedel-Crafts reactions. The -heterocyclic alcohols ionize to produce reactive, dicationic intermediates which provide good to excellent yields of arylation products.
View Article and Find Full Text PDFJ Org Chem
January 2023
Department of Chemistry and Biochemistry, Northern Illinois University, DeKalb, Illinois 60115, United States.
A variety of 9,9'-spirobifluorenes and related azaspirocycles and diazaspirocycles have been prepared in high yields by intramolecular Friedel-Crafts reaction using the Brønsted superacid, triflic acid (CFSOH). Compared to weaker Brønsted acids, the superacid consistently provides better yields along with reduced reaction times and it eliminates the need for heating. The superacid is particularly effective when dicationic electrophilic intermediates are generated in the conversions, for example with the diazaspirocycle syntheses.
View Article and Find Full Text PDFChemistry
May 2022
Aix Marseille Université, CNRS, Centrale Marseille, iSm2 Marseille, Marseille, France.
Enantioenriched complex fused-tricyclic azepanes or bridged-polycyclic azocanes were constructed via a two-step sequence involving an enantioselective organocascade followed by superacid activation of the domino adduct. The activated oxa-bridged azepane acts as a key hidden heptacyclic chiral N-acyl iminium ion triggering a chemo- and diastereoselective intramolecular mono- or di-arylation.
View Article and Find Full Text PDFChemistry
January 2022
IC2MP UMR CNRS 7285, Equipe "Synthèse Organique", Université de Poitiers, 4 rue Michel, Brunet, 86073 Poitiers cedex 9, France.
Under superacid conditions, aromatic amines are directly and regioselectively 1,1-difluoroethylated. Low temperature in situ NMR studies confirmed the presence of benzylic α-fluoronium and α-chloronium ions as key intermediates in the reaction. This method has a wide substrate scope and can be applied to the late-stage functionalization of natural alkaloids and active pharmaceutical ingredients.
View Article and Find Full Text PDFChem Commun (Camb)
July 2020
Research Foundation ITSUU Laboratory, C1232 Kanagawa Science Park R & D Building, 3-2-1 Sakado, Takatsu-ku, Kawasaki, Kanagawa 213-0012, Japan.
Superacid-promoted conversion of tetrahydroisoquinolines to triarylmethanes via tandem reactions of C-N bond scission, Friedel-Crafts alkylation, C-O bond scission, and electrophilic aromatic amidation was developed. Dication formation was important for stabilizing the ring-opened carbocationic intermediate, which is a new role for diprotonation in reaction mechanisms.
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