Palladium‐Catalyzed Annulation of Diarylamines with Olefins through C?H Activation: Direct Access to N‐Arylindoles

A palladium‐catalyzed dehydrogenative coupling between diarylamines and olefins has been discovered for the synthesis of substituted indoles. This intermolecular annulation approach incorporates readily available olefins for the first time and obviates the need of any additional directing group. An ortho palladation, olefin coordination, and β‐migratory insertion sequence has been proposed for the generation of olefinated intermediate, which is found to produce the expected indole moiety.     

Synthesis of Asymmetrically Substituted Terpyridines by Palladium‐Catalyzed Direct C?H Arylation of Pyridine N‐Oxides

The synthesis of asymmetrically substituted 2,2′:6′,2′′‐terpyridines is reported. First, palladium‐catalyzed C? H arylation of pyridine N‐oxides with substituted bromopyridines gave 2,2′‐bipyridine N‐oxides, which were further arylated in a second step to form 2,2′:6′,2′′‐terpyridine N‐oxides. Yields of up to 77 % were obtained with N‐oxides bearing an electron‐withdrawing ethoxycarbonyl substituent in the 4‐position. Pd(OAc)₂ with either P(tBu)₃ or P(o‐tolyl)₃ was used as the catalyst. Cyclometalated complexes derived from Pd(OAc)₂ and these phosphines were also effective. K₃PO₄ as the base gave better results than K₂CO₃. Subsequent deoxygenation with H₂ and Pd/C as the catalyst gave the asymmetrically substituted 2,2′:6′,2′′‐terpyridines in near quantitative yield. This reaction sequence significantly reduces the number of steps required in comparison with known cross‐coupling methods and therefore allows convenient and scalable access to substituted terpyridines.     

Palladium‐Catalyzed Intramolecular C?H Difluoroalkylation: Synthesis of Substituted 3,3‐Difluoro‐2‐oxindoles

The synthesis of 3,3‐difluoro‐2‐oxindoles through a robust and efficient palladium‐catalyzed C H difluoroalkylation is described. This process generates a broad range of difluorooxindoles from readily prepared starting materials. The use of BrettPhos as the ligand was crucial for high efficiency. Preliminary mechanistic studies suggest that oxidative addition is the rate‐determining step for this process.     

Palladium‐Catalyzed Direct C?H Functionalization of Benzoquinone

A direct Pd‐catalyzed C H functionalization of benzoquinone (BQ) can be controlled to give either mono‐ or disubstituted BQ, including the installation of two different groups in a one‐pot procedure. BQ can now be directly functionalized with aryl, heteroaryl, cycloalkyl, and cycloalkene groups and, moreover, the reaction is conducted in environmentally benign water or acetone as solvents.     

Room‐Temperature Palladium‐Catalyzed C?H Activation: ortho‐Carbonylation of Aniline Derivatives

Pd and CO—ureally got me! The title reaction proceeds efficiently at 18 °C under CO (1 atm) with 5 % [Pd(OTs)₂(MeCN)₂] as precatalyst. Depending on the solvents used, either anthranilates or cyclic imides can be obtained in high yields (see picture, BQ=benzoquinone, Ts=4‐toluenesulfonyl).

     

Palladium‐Catalyzed C?H Fluorosilylation of 2‐Phenylpyridines: Synthesis of Silafluorene Equivalents

Treatment of 2‐phenylpyridines with amino(1,3,2‐dioxaborolan‐2‐yl)diphenylsilane produced fluorosilylated 2‐phenylpyridines in good to excellent yields under palladium catalysis. This reaction is the first example of C H fluorosilylation. Single‐crystal X‐ray structure analysis revealed a Lewis acid–base interaction between the silicon and nitrogen atoms, and the obtained fluorosilylated products are silafluorene equivalents. The fluorosilylated products showed stronger fluorescence than the corresponding silafluorene derivative.     

Direct ortho‐Arylation of N‐Phenacylpyridinium Bromide by Palladium‐Catalyzed C?H‐Bond Activation

A novel palladium catalyzed direct ortho‐arylation of N‐phenacylpyridinium bromide was developed. The amazing N‐phenacyl group regioselectively activates the C? H bond of pyridine and automatically departs from the arylated products. A kinetic isotope effect study proved that the reaction went through a C? H‐bond activation pathway and 2,6‐diphenylpyridine was produced stepwise from 2‐phenylpyridine.     

Synthesis of 1,3‐Diamines Through Rhodium‐Catalyzed C?H Insertion

A grand opening : N‐Boc‐N‐alkylsulfamides are effective substrates for the title transformation. Oxidative cyclization is highly chemoselective as well as being both stereospecific and diastereoselective. With the advent of new protocols that facilitate ring opening of the six‐membered‐ring heterocyclic products, access to differentially protected 1,3‐diamines has been made possible (see scheme).

     

Synthesis of 1,3‐Diamines Through Rhodium‐Catalyzed C?H Insertion

Schließen und öffnen : N‐Boc‐N‐alkylsulfamide sind geeignete Substrate für die Titelreaktion. Die oxidative Cyclisierung im ersten Schritt ist hoch chemoselektiv sowie stereospezifisch und diastereoselektiv. Mit neuen Verfahren zur Öffnung der dabei erhaltenen Sechsringheterocyclen werden unterschiedlich geschützte 1,3‐Diamine zugänglich (siehe Schema).

     

Copper‐Catalyzed Regioselective ortho C?H Cyanation of Vinylarenes

A copper‐based catalytic technique for the regioselective ortho C H cyanation of vinylarenes has been developed. This method provides an effective means for the selective functionalization of vinylarene derivatives. A copper‐catalyzed cyanative dearomatization mechanism is proposed to account for the regiochemical course of this reaction.     

Palladium‐Catalyzed Dearomative Cyclocarbonylation by C?N Bond Activation

A fundamentally novel approach to bioactive quinolizinones is based on the palladium‐catalyzed intramolecular cyclocarbonylation of allylamines. [Pd(Xantphos)I₂], which features a very large bite angle, has been found to facilitate the rapid carbonylation of azaarene‐substituted allylamines into bioactive quinolizinones in good to excellent yields. This transformation represents the first dearomative carbonylation and is proposed to proceed by palladium‐catalyzed C N bond activation, dearomatization, CO insertion, and a Heck reaction.