Dialkylbiaryl phosphines are a valuable class of ligand for Pd-catalyzed amination reactions and have been applied in a range of contexts. This perspective attempts to aid the reader in the selection of the best choice of reaction conditions and ligand of this class for the most commonly encountered and practically important substrate combinations.

Dialkylbiaryl phosphines in Pd-catalyzed amination: a user's guide

The Pd-catalyzed coupling of aryl (pseudo)halides and amines is one of the most powerful approaches for the formation of C(sp(2))-N bonds. The pioneering reports from Migita and subsequently Buchwald and Hartwig on the coupling of aminostannanes and aryl bromides rapidly evolved into general and practical tin-free protocols with broad substrate scope, which led to the establishment of what is now known as the Buchwald-Hartwig amination. This Minireview summarizes the evolution of this cross-coupling reaction over the course of the past 25 years and illustrates some of the most recent applications of this well-established methodology.

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The Buchwald–Hartwig Amination After 25 Years

Cyclobutanes and cyclobutenes are important structural motifs found in numerous biologically significant molecules, and they are useful intermediates for chemical synthesis. Consequently, [2+2] cycloadditions to access cyclobutanes and cyclobutenes have been established to be particularly useful transformations. Within the last 10 years, an increase in the frequency of publications for catalytic enantioselective [2+2] cycloadditions has occurred. These reactions provide access to a wide array of enantiomerically enriched chemical diversity that was not previously attainable. Described in this review are the advances made in catalytic enantioselective [2+2] cycloadditions to access cyclobutanes and cyclobutenes.

Cyclobutane and cyclobutene synthesis: catalytic enantioselective [2+2] cycloadditions.

Oxygen-containing heterocycles are an important class of compounds with diverse biological activities. In recent years, direct α-C–H functionalization of inexpensive and abundant readily available ethers and alcohols by oxidative radical cross-coupling with different nucleophilic partners (C–H, N–H, O–H and S–S), leading to the construction of C–C and C–X (X=C, N, O, S) bonds, has emerged as one of the vital strategies among oxidative cross-coupling reactions. Owing to the features of being atom-economic, environmentally benign, having a simple operation and biologically properties, a series of ether α-C(sp3)–H bond activation reactions have been developed by metal or metal-free systems via the radical oxidative coupling pathway, since the radical oxidative coupling reactions have wide range of applications. This review aims to highlight the recent advances in direct α-C(sp3)–H bond functionalization of ethers and alcohols via radical oxidative process.

Recent Advances of Oxidative Radical Cross-Coupling Reactions: Direct α-C(sp3)–H Bond Functionalization of Ethers and Alcohols

Recent advancements in dehydrogenative cross coupling reactions for CC bond formation

A simple α-C–H amination of cyclic ether with indole/carbazole derivatives has been accomplished by employing copper(II) chloride/bipy as the catalyst system. In the presence of the di-tert-butyl peroxide oxidant, cyclic ethers such as tetrahydrofuran, 1,4-dioxane, and tetrahydropyran successfully undergo C–H/N–H cross dehydrogenative coupling (CDC) with various carbazole or indole derivatives in good-to-excellent yields.

Copper-Catalyzed Oxidative C-H Amination of Tetrahydrofuran with Indole/Carbazole Derivatives.

Cross-dehydrogenative-coupling (CDC) between C–H/C–H bonds of indoles and cyclic ethers/cycloalkanes is made viable through a simple transition-metal-free pathway. With the aid of only di-tert-butyl peroxide, a number of inactive cyclic ethers and cycloalkanes can be directly coupled with indole derivatives in satisfactory yields.

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Oxidative coupling between C(sp2)–H and C(sp3)–H bonds of indoles and cyclic ethers/cycloalkanes

Oxabenzonorbornadienes were found to be suitable substrates for asymmetric hydroalkynylation reactions. Catalyzed by the complex of [Ir(COD)Cl](2) and (R)-SYNPHOS, oxabenzonorbornadienes and terminal alkynes could react smoothly to give the alkynylated products in moderate to good yields (up to 93% yield) and enantioselectivities (up to 85% ee).

Qingjing Yang

Papers

Copper-Catalyzed Oxidative C-H Amination of Tetrahydrofuran with Indole/Carbazole Derivatives.

Oxidative coupling between C(sp2)–H and C(sp3)–H bonds of indoles and cyclic ethers/cycloalkanes

Iridium-catalyzed asymmetric hydroalkynylation reactions of oxabenzonorbornadienes

Rh-Catalyzed Highly Enantioselective Hydroalkynylation Reaction of Norbornadiene Derivatives

Catalytic Asymmetric Syntheses of 2‐Aryl Chromenes