Dual Gold Catalysis: Bidirectional Processes and Tandem sp³‐C−H Insertion Reactions

Abstract

Various tetrayne systemsw erec onverted under dual gold-catalyzedc onditions. For symmetric tetraalkynylsubstitutedt hiophenes, bearing two alkyl-substituted alkynes and two terminal alkyne units, bidirectionalc yclizations led to the efficient formation of dibenzothiophene systems. In all cases, selective CH activation of the CÀHb ond of the alkyl substituent was observed leading to cyclopentane moieties annelated to the newly formed aromatic cores. If two thiophene moieties were tethered over the attached non-terminal alkynes, depending on the length of the connectinga lkyl tether,e ither bidirectionalp rocesses or tandem processes can be addressed leadingt oi nteresting molecular structures, such as spiro compoundso ri solated benzothiophenesc onnected by aC ÀCb ond. Other electron-rich heterocycles also reacted. While the reactions even worked for some mixed systems, other cases only delivered the products of amono-cyclization.

Homogeneous and Heterogeneous Gold Catalysis for Materials Science

“…This different reactivity was also studied in a bidirectional approach in 2017 with tetraalkynyl-substituted thiophenes bearing a thiophene core . These tetraynes with two alkyl-substituted alkynes and two terminal alkyne units led to dibenzothiophene systems very efficiently.…”

Catalytic Gold Chemistry: From Simple Salts to Complexes for Regioselective C−H Bond Functionalization

“…Another example of selective 6-endo-dig cyclization under dual activation catalysis in a bidirectional manner was noted in the use of tetrayne substituted thiophenes to prepare dibenzothiophene derivatives. [292] In these substrates, the Csp 3 À H bond at the γposition of alkyl side chain was selectively activated, leading to annulation of a cyclopentane ring to the newly formed benzene ring. As opposed to the above-mentioned examples which generally possess a γ-Csp 3 À H bond on the alkyl side chain, substrates lacking γ-Csp 3 hydrogen atoms were also shown to undergo cyclizations by gold-catalyzed dual activation.…”

“…This scenario precludes the alternative vinylidene pathway which would lead to regioisomeric 5‐ endo ‐ dig products. Another example of selective 6‐ endo ‐ dig cyclization under dual activation catalysis in a bidirectional manner was noted in the use of tetrayne substituted thiophenes to prepare dibenzothiophene derivatives [292] . In these substrates, the Csp 3 −H bond at the γ‐position of alkyl side chain was selectively activated, leading to annulation of a cyclopentane ring to the newly formed benzene ring.…”

Advances and Prospects in Gold‐Catalyzed C−H Activation

“…Hashmi and coworkers successfully carried out bidirectional cyclization of thiophene‐tethered tetraynes 196 in the presence of dual activated gold catalyst (DAC) to generate polycyclic dibenzothiophene derivatives 197 (Scheme ) . The protocol was applied to a wide variety of substrates including pyridinium salts, vinyl tethered substrates, thiophene cores etc and obtained good yields under the optimized reaction conditions.…”