External oxidant-free alkylation of quinoline and pyridine derivatives

Metal-organic framework boosts heterogeneous electron donor-acceptor catalysis

Metal-organic framework (MOF) is a class of porous materials providing an excellent platform for engineering heterogeneous catalysis. We herein report the design of MOF Zr-PZDB consisting of Zr6-clusters and PZDB (PZDB = 4,4'-(phenazine-5,10-diyl)dibenzoate) linkers, which served as the heterogeneous donor catalyst for enhanced electron donor-acceptor (EDA) photoactivation. The high local concentration of dihydrophenazine active centers in Zr-PZDB can promote the EDA interaction, therefore resulting in superior catalytic performance over homogeneous counterparts. The crowded environment of Zr-PZDB can protect the dihydrophenazine active center from being attacked by radical species. Zr-PZDB efficiently catalyzes the Minisci-type reaction of N-heterocycles with a series of C-H coupling partners, including ethers, alcohols, non-activated alkanes, amides, and aldehydes. Zr-PZDB also enables the coupling reaction of aryl sulfonium salts with heterocycles. The catalytic activity of Zr-PZDB extends to late-stage functionalization of bioactive and drug molecules, including Nikethamide, Admiral, and Myristyl Nicotinate. Systematical spectroscopy study and analysis support the EDA interaction between Zr-PZDB and pyridinium salt or aryl sulfonium salt, respectively. Photoactivation of the MOF-based EDA adduct triggers an intra-complex single electron transfer from donor to acceptor, giving open-shell radical species for cross-coupling reactions. This research represents the first example of MOF-enabled heterogeneous EDA photoactivation.

Copper-promoted difunctionalization of unactivated alkenes with silanes

An efficient copper-catalyzed cascade difunctionalization of N-allyl anilines toward the synthesis of silylated indolines using commercially available silanes has been reported. This strategy provides a new avenue for the synthesis of a diverse array of indolines in reasonable yields. Preliminary mechanistic investigations indicate that the reaction probably proceeds via a radical pathway with unactivated alkenes as radical acceptors and simple silanes as radical precursors. This protocol is distinguished by its atom economy, broad substrate scope and readily available starting materials.

α-Csp3–H Bond Functionalization of Simple Ethers in Radical Reactions

The direct α-Csp3–H functionalization of simple ethers is a vital strategy among radical reactions. This review discusses their applications according to the starting materials: (1) reactions with alkenes or alkynes; (2) reactions with other unsaturated compounds; and (3) reactions with nucleophilic partners. Mechanisms like radical addition, C–H activation, elimination, metal-catalyzed coupling, cyclization, oxidation, and rearrangement will be analyzed herein.

1 Introduction

2 Reactions with Alkenes or Alkynes

3 Reactions with Other Unsaturated Compounds

4 Reactions with Nucleophilic Partners

5 Oxidation of Ethers

6 Conclusions

Metal-Free Alkylation of Quinoxalinones with Aryl Alkyl ketones

The first metal-free method for alkylation of quinoxalinones using cheap and stable aryl alkyl ketones as nucleophilic alkylation reagents is reported. This strategy greatly broadens the application channels of aryl...

Radical chain monoalkylation of pyridines

The monoalkylation of N-methoxypyridinium salts with alkyl radicals generated from alkenes (via hydroboration with catecholborane), alkyl iodides (via iodine atom transfer) and xanthates is reported. The reaction proceeds under neutral conditions since no acid is needed to activate the heterocycle and no external oxidant is required. A rate constant for the addition of a primary radical to N-methoxylepidinium >10⁷ M^-1 s^-1 was experimentally determined. This rate constant is more than one order of magnitude larger than the one measured for the addition of primary alkyl radicals to protonated lepidine demonstrating the remarkable reactivity of methoxypyridinium salts towards radicals. The reaction has been used for the preparation of unique pyridinylated terpenoids and was extended to a three-component carbopyridinylation of electron-rich alkenes including enol esters, enol ethers and enamides.