On the Gold‐Catalyzed Intramolecular 7‐exo‐trig Hydroamination of Allenes

Abstract

Aniline derivatives with allene side tethers were tested as substrates for a gold-catalyzed 7-exotrig hydroamination reaction. The nucleophilicity of the aniline derivatives plays an important role for the outcome of the reaction. While electron-deficient protecting groups at the nitrogen led to competing pathways like hydroarylation or an allene to diene isomerization, clean formation of the desired benzoxazepines was obtained with unprotected aniline derivatives.Chemicals were purchased from commercial suppliers and used without further purification. Dry solvents were dispensed from the solvent purification system MB SPS-800. NMR spectra were, if not mentioned otherwise, recorded at room temperature on the following spectrometers: Bruker ARX-250, Bruker Avance DRX-300, Bruker Avance III-Scheme 7. Summary of the possible pathways for anilines 5 or 8.

Recent Progress in N-Heterocyclic Carbene Gold-Catalyzed Reactions of Alkynes Involving Oxidation/Amination/Cycloaddition

“…Firstly, intramolecular nucleophilic addition of the azide onto the NHC gold-activated species readily occurred, thus forming the α-imino gold carbenes 32-A, which were trapped quickly by an intermolecular O-H insertion to generate the 3-alkynyloxyindoles 32-B. Subsequent Saucy-Marbet rearrangement uniquely took place to deliver smoothly the allenes 32-C [91], followed by an intramolecular hydroamination reaction, catalyzed by the same NHC gold complex [92][93][94][95][96][97], to yield the final pyrroloindolone derivatives 34. Gong et al gave a plausible mechanism for the formation of pyrroloindolone derivatives 34 (Scheme 21).…”

On the Nature of Interactions between Ionic Liquids and Small Amino‐Acid‐Based Biomolecules

“…During the last decade, gold catalysis has shown its supremacy in activations of unsaturated C–C bonds towards various nucleophiles 15. One valuable invention has been the syntheses of nitrogen heterocycles through gold‐catalyzed hydroamination of internal alkynes, allenes and alkenes with primary and secondary amines as expedient nucleophiles 16. Pioneering work in this area was reported by Utimoto and co‐workers, who successfully accomplished the cycloisomerization of aminoalkynes to form tetrahydropyridines by NaAuCl 4 catalysis 17.…”

Mechanistic Insights into the Post‐Cyclization Isomerization in Gold‐Catalyzed 7‐exo‐dig‐Hydroarylations

“…For this purpose, trifluoroacetic acid (TFA)-protected aniline was tested as possible weak base (but still strong enough to capture the proton of the in situ formed HNTf 2 ), whichd oes allow reactions at room temperature. [10] Catalyst B (0.5 mol %) and the aniline (5 mol %) were used in CD 2 Cl 2 at room temperature. After 24 hours, complete conversion was achieved giving am ixture of 2a and 3a in 99 %y ield, determined by NMR spectroscopy,a nd as electivity for 3a of 8:1.…”