Katalytische, isofunktionelle Reaktionen – Erweiterung des Repertoires an Shuttle‐ und Metathesereaktionen

Controlling Selectivity in Shuttle Hetero-difunctionalization Reactions: Electrochemical Transfer Halo-thiolation of Alkynes

Shuttle hetero-difunctionalization reaction, in which two chemically distinct functional groups are transferred between two molecules, has long been an unmet goal due to the daunting challenges in controlling the chemo-, regio-, and stereoselectivity. Herein, we disclose an electrochemistry enabled shuttle reaction (e-shuttle) to selectively transfer one RS^- and one X^- group between β-halosulfides and unsaturated hydrocarbons via a consecutive paired electrolysis mechanism. The preferential anodic oxidation of one anion over the other, which is controlled by their distinct redox potentials, plays a pivotal role in controlling the high chemoselectivity of the process. This easily scalable methodology enables the construction of a myriad of densely functionalized β-halo alkenyl sulfides in unprecedented chemo-, regio-, and stereoselectivity using benign surrogates, e.g., 2-bromoethyl sulfide, avoiding the handling of corrosive and oxidative RS-Br reagents. In a broader context, these results open up new strategies for selective shuttle difunctionalization reactions.

Silicon Catalyzed C-O Bond Ring Closing Metathesis of Polyethers

The Lewis superacid bis(perchlorocatecholato)silane catalyzes C-O bond metathesis of alkyl ethers with an efficiency outperforming all earlier reported systems. Chemoselective ring contractions of macrocyclic crown ethers enable substrate-specific transformations, and an unprecedented ring-closing metathesis of polyethylene glycols allows polymer-selective degradation. Quantum chemical computations scrutinize a high Lewis acidity paired with a simultaneous low propensity for polydentate substrate binding as critical for successful catalysis. Based on these mechanistic insights, a second-generation class of silicon Lewis superacid with enhanced efficacy is identified and demonstrated.

Alternating Current Electrolysis Enabled Formal C-O/O-H Cross-Metathesis of 4-Alkoxy Anilines with Alcohols

While multiple bond metathesis reactions, for example olefin metathesis, have seen considerable recent progress, direct metathesis of traditionally inert C-O single bonds is extremely rare and particularly challenging. Undoubtedly, metathesis reaction of C-O bonds is one of the most ideal routes for the value-added upgrading of molecules involving C-O bonds. Reported here is a new protocol to achieve the formal C-O/O-H cross-metathesis via alternating current electrolysis. Featuring mild reaction conditions, the protocol allows readily available 4-alkoxy anilines and alcohols to be converted into a wide range of valuable products in highly regioselective and chemoselective manner. Moreover, the present strategy can be used in the late-stage modification of pharmaceuticals as well as biologically active compounds, which demonstrated the potential application.

Iron-Catalyzed Reductive Cyclization by Hydromagnesiation: A Modular Strategy Towards N-Heterocycles

A reductive cyclization to prepare a variety of N-heterocycles, through the use of ortho-vinylanilides, is reported. The reaction is catalyzed by an inexpensive and bench-stable iron complex and generally occurs at ambient temperature. The transformation likely proceeds through hydromagnesiation of the vinyl group, and trapping of the in situ generated benzylic anion by an intramolecular electrophile to form the heterocycle. This iron-catalyzed strategy was shown to be broadly applicable and was utilized in the synthesis of substituted indoles, oxindoles and tetrahydrobenzoazepinoindolone derivatives. Mechanistic studies indicated that the reversibility of the hydride transfer step depends on the reactivity of the tethered electrophile. The synthetic utility of our approach was further demonstrated by the formal synthesis of a reported bioactive compound and a family of natural products.

Nickel-Catalyzed Thiolation of Aryl Nitriles

A nickel-catalyzed thiolation of aryl nitriles has been developed to access functionalized aryl thioethers. The ligand dcype (1,2-bis(dicyclohexylphosphino)ethane) as well as the base KOt Bu (potassium tert-butoxide) are essential to achieve this transformation. This scalable and practical process involves both a C-C bond activation and a C-S bond formation. Furthermore, this reaction shows a high functional-group tolerance and enables the late-stage functionalization of important molecules.

Nickel-Catalyzed Inter- and Intramolecular Aryl Thioether Metathesis by Reversible Arylation

A nickel‐catalyzed aryl thioether metathesis has been developed to access high‐value thioethers. 1,2‐Bis(dicyclohexylphosphino)ethane (dcype) is essential to promote this highly functional‐group‐tolerant reaction. Furthermore, synthetically challenging macrocycles could be obtained in good yield in an unusual example of ring‐closing metathesis that does not involve alkene bonds. In‐depth organometallic studies support a reversible Ni⁰/Ni^II pathway to product formation. Overall, this work not only provides a more sustainable alternative to previous catalytic systems based on Pd, but also presents new applications and mechanistic information that are highly relevant to the further development and application of unusual single‐bond metathesis reactions.