Highly Stereoselective Assembly of Polycyclic Molecules from 1,6-Enynes Triggered by Rhodium(III)-Catalyzed C–H Activation

Abstract

An Rh(III)-catalyzed C-H activation of pyrazolones with 1,6-enynes was investigated. The regioselectivity of the C-H activation/alkyne insertion is readily solved by using symmetric enyne coupling partners, and a C-H activation-triggered cascade reaction is realized, which involves alkyne insertion, tautomerization, and double cyclization to offer a class of structurally complex polycyclic architectures. This cascade reaction tolerates a broad substrate scope in high regioselectivity and stereospecificity and furnishes three new chemical bonds and four chiral centers in a single operation. Various derivatizations of the polycyclic scaffolds are conducted, providing products with ample space for further functional transformations.

Propargylic Alcohols as Coupling Partners in Transition‐Metal‐Catalyzed Arene C−H Activation

“…In 2018, Zhang et al [14] accounted for the synthesis of highly stereoselective polycyclic molecules from desymmetrization of 1,6-enynes through Rh-catalyzed CÀ H functionalization of N-aryl pyrazol-5-one approach. This desymmetrizative annulation path was proposed as depicted in Scheme 10, with some exper- imental evidence.…”

“…In 2018, Zhang et al [14] . accounted for the synthesis of highly stereoselective polycyclic molecules from desymmetrization of 1,6‐enynes through Rh‐catalyzed C−H functionalization of N‐aryl pyrazol‐5‐one approach.…”

Rh(III)-Catalyzed C–H Bond Activation for the Construction of Heterocycles with sp3-Carbon Centers

“…The approaches to access them via transition-metal-catalyzed C-H bond activation are particularly impressive, because these products are highly congested scaffolds difficult to access through traditional methods. Zhang's group in 2018 developed an Rh(III)-catalyzed C−H bond activation strategy to assemble pyrazolones with 1,6-enynes to access fused-chromene scaffolds (Scheme 27) [107]. This cascade reaction ranged a broad substrate scope in high regioselectivity and stereospecificity and furnished three new chemical bonds and four chiral centers in a single operation.…”

The oxidative coupling between benzaldehyde derivatives and phenylacetylene catalyzed by rhodium complexes via C-H bond activation

“…Even if Rh catalysts are expensive, they have unique advantages because of their functional group tolerance, wide range of substrate scope, high activity, and selectivity for synthetic transformations [22][23][24][25][26]. Rh catalysts are used by many researchers in C-H activation reactions [27][28][29]. One kind of Rh catalyst, which contains Cp* (Cp* = 1,2,3,4,5-Pentamethylcyclopentadiene (C 5 Me 5 ) ligands, has been used to catalyze oxidative coupling reactions.…”

“…One kind of Rh catalyst, which contains Cp* (Cp* = 1,2,3,4,5-Pentamethylcyclopentadiene (C 5 Me 5 ) ligands, has been used to catalyze oxidative coupling reactions. For example, Lu et al reported that [Cp*RhCl 2 ] 2 catalyzed the C-H activation of pyrazolones with symmetric 1,6-enynes to obtain functional products in 34%-72% yield [27]. Krieger's team used [Cp*RhCl 2 ] 2 to obtain macrocyclic pyridones in excellent yields, and proposed that the catalyst could become more efficient in redox-neutral processes when the O-pivaloyl hydroxamate is the directing group [28].…”