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Evidence for Alkene cis ‐Aminocupration, an Aminooxygenation Case Study: Kinetics, EPR Spectroscopy, and DFT Calculations
Author(s) -
Paderes Monissa C.,
Belding Lee,
Fanovic Branden,
Dudding Travis,
Keister Jerome B.,
Chemler Sherry R.
Publication year - 2012
Publication title -
chemistry – a european journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.687
H-Index - 242
eISSN - 1521-3765
pISSN - 0947-6539
DOI - 10.1002/chem.201101703
Subject(s) - alkene , chemistry , intramolecular force , carboxylate , olefin fiber , electron paramagnetic resonance , reaction mechanism , copper , photochemistry , concerted reaction , kinetic isotope effect , catalysis , medicinal chemistry , stereochemistry , organic chemistry , physics , nuclear magnetic resonance , deuterium , quantum mechanics
Alkene difunctionalization reactions are important in organic synthesis. We have recently shown that copper(II) complexes can promote and catalyze intramolecular alkene aminooxygenation, carboamination, and diamination reactions. In this contribution, we report a combined experimental and theoretical examination of the mechanism of the copper(II)‐promoted olefin aminooxygenation reaction. Kinetics experiments revealed a mechanistic pathway involving an equilibrium reaction between a copper(II) carboxylate complex and the γ‐alkenyl sulfonamide substrate and a rate‐limiting intramolecular cis ‐addition of NCu across the olefin. Kinetic isotope effect studies support that the cis ‐aminocupration is the rate‐determining step. UV/Vis spectra support a role for the base in the break‐up of copper(II) carboxylate dimer to monomeric species. Electron paramagnetic resonance (EPR) spectra provide evidence for a kinetically competent NCu intermediate with a Cu II oxidation state. Due to the highly similar stereochemical and reactivity trends among the Cu II ‐promoted and catalyzed alkene difunctionalization reactions we have developed, the cis ‐aminocupration mechanism can reasonably be generalized across the reaction class. The methods and findings disclosed in this report should also prove valuable to the mechanism analysis and optimization of other copper(II) carboxylate promoted reactions, especially those that take place in aprotic organic solvents.