Inter‐ and Intramolecular Hydroamination of Unactivated Alkenes Catalysed by a Combination of Copper and Silver Salts: The Unveiling of a Brønstedt Acid Catalysis

Abstract

Abstract:The combined use of a copper halide, a silver salt and a phosphane ligand was applied for the catalysis of inter-and intramolecular hydroamination of alkenes. The reactions of unactivated olefins with nitrogen substrates were investigated. Mechanistic investigations demonstrated that the catalytic system generated a Brønsted acid which appeared to be the prominent catalytic species.

A Commercially Available and User‐Friendly Catalyst for Hydroamination Reactions under Technical Conditions

“…Although unlikely because of the use of a primary amine, a control experiment with HBF 4 ruled out any Brønsted acid catalysis under these conditions (Table , entry 4) . With acetonitrile as the solvent of choice, the scope of the reaction was next explored at 80 °C with copper loadings ranging from 2 to 20 mol‐%.…”

Synthesis of Saturated Heterocycles via Metal-Catalyzed Alkene Hydroamination or Hydroalkoxylation Reactions

“…While reports have begun to emerge over the last 10 years for copper-catalyzed inter-and intramolecular hydroaminations, typically either activated olefins or electron-deficient N-protected amines are required for reactions to proceed [61,62]. Furthermore, Bronsted acid-catalyzed mechanisms have been typically invoked for processes employing Cu(II) salts [9,63]. To date, there are only two reports of copper-catalyzed intramolecular hydroaminations of basic amines onto tethered unactivated olefins [63,64].…”

“…A cationic copper complex generated from CuBr 2 , dppe (diphenylphosphinoethane), and AgBF 4 catalyzes the hydroamination of secondary alkylamines 79 onto unactivated olefins (Scheme 35) [63]. The substrate scope is limited to secondary amine substrates containing gem-disubstitution on the alkyl linker.…”

“…Furthermore, Bronsted acid-catalyzed mechanisms have been typically invoked for processes employing Cu(II) salts [9,63]. To date, there are only two reports of copper-catalyzed intramolecular hydroaminations of basic amines onto tethered unactivated olefins [63,64]. In 2009, Sawamura and coworkers reported the use of a Cu(Ot-Bu)-xantphos complex as an efficient catalyst for the hydroamination of both primary and secondary aminoalkene substrates 74 to afford five-and six-membered ring products 75 (Scheme 33) [64].…”

Iron‐Catalyzed Anti‐Markovnikov Hydroamination of Vinylpyridines

“…[11] More recently,acombinationo f copper and silver salts was used to catalyze the hydroamination of vinylpyridines and the weak base tosylamine, buto nly in 16 %y ield. [12] Therefore, an ew synthetic strategy for anti-Markovnikovh ydroamination of vinylpyridines and weaker amines with high yields and regioselectivities is needed.…”