C-H-Funktionalisierung durch eine intramolekulare Redox-Strategie

EATA Reaction Catalyzed by Copper Halides of Mixed Oxidation States and Its Application to Total Synthesis of Scorodonin

Naturally occurring conjugated allenynes are of general interest to the scientific community for their potent and various biological activities. The 1,5-H transfer of alka-1,4-diyn-3-yl amines would be one of the most straightforward yet challenging approach to this class of compounds since it may, in principle, form two regioisomeric products involving two different C-C triple bonds. Herein, a catalytic recipe of copper halides with mixed oxidation states, i.e., CuCl/CuBr 2 , has been identified to address the issues of the side reaction of conjugate addition and the selectivity of 1,5-H transfer of the key intermediate, alka-1,4-diyn-3-yl amines, in EATA (Enantioselective Allenation of Terminal Alkynes) reaction involving the conjugated 2-alkynals. This protocol could accommodate a wide range of functional groups providing a series of allenynes with a very high enantioselectivity (up to >99% ee). In addition, the enantioenriched allenynes can be readily transformed into various building blocks and applied to the highly enantioselective total synthesis of linear allenic natural product scorodonin for the first time. Mechanistic studies and DFT calculations elucidated the high regioselectivity for observed 1,5-H transfer within the intermediate of 1,4-diyn-3-yl amines. The calculated energy difference between two of the most stable transition states of 3.4 kcal/mol accounts for a selectivity of over 99:1, which is in perfect agreement with the experimental results.

Redox-Neutral Aromatization of Cyclic Amines: Mechanistic Insights and Harnessing of Reactive Intermediates for Amine α- and β-C-H Functionalization

Cyclic amines such as pyrrolidine and piperidine are known to undergo condensations with aldehydes to furnish pyrrole and pyridine derivatives, respectively. A combined experimental and computational study provides detailed insights into the mechanism of pyrrole formation. A number of reactive intermediates (e.g., azomethine ylides, conjugated azomethine ylides, enamines) were intercepted, outlining strategies for circumventing aromatization as a valuable pathway for amine C-H functionalization.

Harnessing the Electrophilicity of Keteniminium Ions: A Simple and Straightforward Entry to Tetrahydropyridines and Piperidines from Ynamides

An efficient, modular and straightforward entry to tetrahydropyridines and piperidines is reported. This reaction is based on a formal intramolecular hydroalkylation of readily available, properly substituted ynamides which, upon simple activation under acidic conditions, generate highly reactive activated keteniminium ions whose reactivity can be finely controlled to induce a remarkably efficient [1,5]-hydride shift from unactivated C-H bonds and trigger a cationic cyclization which is complete within minutes.

Intramolecular Redox-Mannich Reactions: Facile Access to the Tetrahydroprotoberberine Core

Cyclic amines such as pyrrolidine undergo redox-annulations with 2-formylaryl malonates. Concurrent oxidative amine α-CH bond functionalization and reductive N-alkylation render this transformation redox-neutral. This redox-Mannich process provides regioisomers of classic Reinhoudt reaction products as an entry to the tetrahydroprotoberberine core, enabling the synthesis of (±)-thalictricavine and its epimer. An unusually mild amine-promoted dealkoxycarbonylation was discovered in the course of these studies.

Redox-neutral α,β-difunctionalization of cyclic amines

In contrast to the continuously growing number of methods that allow for the efficient α-functionalization of amines, few strategies exist that enable the direct functionalization of amines in the β-position. A general redox-neutral strategy is outlined for amine β-functionalization and α,β-difunctionalization that utilizes enamines generated in situ. This concept is demonstrated in the context of preparing polycyclic N,O-acetals from simple 1-(aminomethyl)-β-naphthols and 2-(aminomethyl)-phenols.

Redox-neutral copper(II) carboxylate catalyzed α-alkynylation of amines

A new strategy for iminium ion isomerization was applied to the direct, redox-neutral α-alkynylation of amines. Cu(II) 2-ethylhexanoate was identified as the optimal catalyst for this three-component coupling reaction of secondary amines, aldehydes and alkynes.