Selective C(sp3 )-N Bond Cleavage of N,N-Dialkyl Tertiary Amines with the Loss of a Large Alkyl Group via an SN 1 Pathway

Polar disconnection of the C(sp³ )-N bond of N,N-dialkyl-substituted tertiary amines via ammonium species conventionally favored the loss of the smaller alkyl group by an S_N 2 displacement, while selective C(sp³ )-N bond cleavage by cutting off the larger alkyl group is still underdeveloped. Herein, we present a novel Pd⁰ -catalyzed [2+2+1] annulation, proceeding through an alkyne-directed palladacycle formation and consecutive diamination with a tertiary hydroxylamine by cleaving its N-O bond and one C(sp³ )-N bond, for the rapid assembly of tricyclic indoles in a single-step transformation. Noteworthy, experimental results indicated that large tert-butyl and benzyl groups were selectively cleaved via an S_N 1 pathway, in the presence of a smaller alkyl group (Me, Et, ⁱ Pr). Under the guidance of this new finding, tricyclic indoles bearing a removable alkyl group could be exclusively obtained by using a (α-methyl)benzyl/benzyl or tert-butyl/2-(methoxycarbonyl)ethyl mixed amino source.

Synthesis of Indoles via Intermolecular and Intramolecular Cyclization by Using Palladium-Based Catalysts

As part of natural products or biologically active compounds, the synthesis of nitrogen-containing heterocycles is becoming incredibly valuable. Palladium is a transition metal that is widely utilized as a catalyst to facilitate carbon-carbon and carbon-heteroatom coupling; it is used in the synthesis of various heterocycles. This review includes the twelve years of successful indole synthesis using various palladium catalysts to establish carbon-carbon or carbon-nitrogen coupling, as well as the conditions that have been optimized.

Synthesis of Indoles through Domino Reactions of 2-Fluorotoluenes and Nitriles

Indoles are essential heterocycles in medicinal chemistry, and therefore, novel and efficient approaches to their synthesis are in high demand. Among indoles, 2-aryl indoles have been described as privileged scaffolds. Advanced herein is a straightforward, practical, and transition-metal-free assembly of 2-aryl indoles. Simply combining readily available 2-fluorotoluenes, nitriles, LiN(SiMe₃ )₂ , and CsF enables the generation of a diverse array of indoles (38 examples, 48-92 % yield). A range of substituents can be introduced into each position of the indole backbone (C4 to C7, and aryl groups at C2), providing handles for further elaboration.

Enantioselective Cross-Exchange between C-I and C-C σ Bonds

A palladium-catalyzed enantioselective intramolecular σ-bond cross-exchange between C-I and C-C bonds is realized, providing chiral indanones bearing an alkyl iodide group and an all-carbon quaternary stereocenter. Pd/TADDOL-derived phosphoramidite is found to be an efficient catalytic system for both C-C bond cleavage and alkyl iodide reductive elimination. In addition to aryl iodides, aryl bromides can also be used for this transformation in the presence of KI. Density-functional theory (DFT) calculation studies support the ring-opening of cyclobutanones occuring through an oxidative addition/reductive elimination process involving Pd^IV species.