A highly diastereoselective method for the synthesis of dihydroepoxybenzofluorenone derivatives from aromatic/vinylic amides and bicyclic alkenes is described. This new transformation proceeds ...through cobalt‐catalyzed C−H activation and intramolecular nucleophilic addition to the amide functional group. Transition‐metal‐catalyzed C−H activation reactions of secondary amides with alkenes usually lead to 4+2 or 4+1 annulation; to the best of our knowledge, this is the first time that a 3+2 cycloaddition is described in this context. The reaction proceeds under mild conditions and tolerates a wide range of functional groups. Mechanistic studies imply that the C−H bond cleavage may be the rate‐limiting step.
3+2 instead of 4+2 or 4+1: The diastereoselective 3+2 annulation of secondary amides with alkenes proceeds by cobalt‐catalyzed C−H activation and intramolecular nucleophilic addition to the amide functional group under mild conditions. Mechanistic studies suggest that the C−H bond cleavage is the rate‐limiting step.
Considerable research attention has been directed towards the use of first‐row transition metals in organic synthesis. The more abundant, and less expensive cobalt is considered to be an effective ...alternative for expensive second and third‐row noble metals, especially in C−H bond functionalization reactions. In this Minireview, we will summarize the features, and recent achievements of the Co‐catalyzed directing group assisted C−H activation/cyclization reactions and their mechanistic insights.
Cost‐effective cobalt: Highly cost‐effective and abundant, Co‐catalyzed C−H functionalization reactions have been developed that efficiently replaces the expensive noble metals in C−H bond activation reactions. This Minireview summarizes the recently emerged high‐valent CoIII‐catalyzed C−H activation/annulation strategies for the construction of heteroaromatic structures. Substantial mechanistic details and future challenges in this research field also have been discussed.
Many steps make light work: Substituted phenanthridinones can be obtained with high regioselectivity and in very good yields by palladium‐catalyzed cyclization reactions of N‐methoxybenzamides with ...arenes (see scheme). The reaction proceeds through multiple oxidative CH activation and CC/CN formation steps in one pot at room temperature, and thus provides a simple method for generating bioactive phenanthridinones.
Four cobalt‐catalyzed oxidative annulation reactions of nitrogen‐containing arenes with alkynes proceeds by C−H activation, thus leading to biologically useful quaternary ammonium salts, including ...pyridoisoquinolinium, cinnolinium, isoquinolinium, and quinolizinium salts, in high yields. The results are comparable to those reactions catalyzed by rhodium and ruthenium complexes. The transformation of the salts into various N‐heterocycles has also been demonstrated.
Salty rings: Four oxidative annulation reactions of arenes with alkynes proceeds through cobalt‐catalyzed pyridine‐, azo‐, and imine‐ directed ortho C−H activation to synthesize various heterocyclic ammonium salts. The reactions tolerate a wide substrate scope and preliminary mechanistic studies are discussed.
It's worth its salt: The title reaction leads to the synthesis of highly substituted isoquinolinium salts (see scheme; Cp*=Me5C5). The reaction proceeds through a CH activation and a subsequent ...annulation in the presence of a rhodium catalyst. The reaction mechanism is discussed as well as its application to the synthesis of the natural product oxychelerythrine.
Versatile salts: A new rhodium‐catalyzed synthesis of cinnolinium salts from various azobenzenes and alkynes under air is described. These salts readily transform into three important classes of ...products, including indoles, indoloindoles, and cinnolines (see scheme).
Ketones and alkynes join together: The catalytic title reaction proceeds rapidly at 120 °C and requires only 1 hour for completion (see scheme). The reaction mechanism likely involves ...chelation‐assisted ortho CH activation, insertion of the alkyne moiety, carbocyclization, and protonation. Cp*=pentamethylcyclopentadienyl.
The bipolar host material BCPO (bis‐4‐ (N‐carbazolyl)phenylphosphine oxide) containing a phosphine oxide and two carbazole groups, synthesized in three steps, shows a high triplet energy gap of 3.01 ...eV. The material can be used as a universal host for blue, green, and red phosphorescent devices, all giving extremely high efficiencies with turn‐on voltages within 3 V.
A regioselective synthesis of indoles from arylhydrazine hydrochlorides with alkynes and diethyl ketone catalyzed by a rhodium complex is described. A possible mechanism involving an in‐situ ...generated oxidizing directing group NNCR1R2 assisted ortho‐CH activation and reductive elimination are proposed. The catalytic reaction is highly compatible with a wide range of functional arylhydrazines and alkynes. The reaction proceeds under mild reaction conditions and is atom‐step economical.
Highly efficient thermally activated delayed fluorescence (TADF) molecules are in urgent demand for solid‐state lighting and full‐color displays. Here, the design and synthesis of three ...triarylamine‐pyridine‐carbonitrile‐based TADF compounds, TPAPPC, TPAmPPC, and tTPAmPPC, are shown. They exhibit excellent photoluminescence quantum yields of 79−100% with small ΔEST values, fast reverse intersystem crossing (RISC), and high horizontal dipole ratios (Θ// = 86−88%) in the thin films leading to the enhancement of device light outcoupling. Consequently, a green organic light‐emitting diode (OLED) based on TPAmPPC shows a high average external quantum efficiency of 38.8 ± 0.6%, a current efficiency of 130.1 ± 2.1 cd A–1, and a power efficiency of 136.3 ± 2.2 lm W–1. The highest device efficiency of 39.8% appears to be record‐breaking among TADF‐based OLEDs to date. In addition, the TPAmPPC‐based device shows superior operation lifetime and high‐temperature resistance. It is worth noting that the TPA‐PPC‐based materials have excellent optical properties and the potential for making them strong candidates for TADF practical application.
Three 2,6‐diphenylpyridine‐3,5‐dicarbonitrile‐based compounds with excellent photoluminescent quantum yields (79–100%) and high horizontal dipole ratios (86−88%) in the thin films are demonstrated. With two methyl groups on the triarylamines, the spin−orbit coupling is enhanced due to the elevated locally excited triplet states (3LE), leading to a fast reverse intersystem crossing. Green thermally activated delayed fluorescence (TADF) organic light‐emitting diodes based on them exhibit a record‐high external quantum efficiency of 39.8% without any optical extraction technique.
![Diastereoselective [3+2] An...](http://api.summon.serialssolutions.com/2.0.0/image/issn/XR4PS5YY4K/1433-7851/small "Diastereoselective [3+2] Annulation of Aromatic/Vinylic Amides with Bicyclic Alkenes through Cobalt-Catalyzed C−H Activation and Intramolecular Nucleophilic Addition")
