Palladium-Catalyzed Controllable Reductive/Oxidative Heck Coupling between Cyclic Enones and Thiophenes via C–H Activation

Photoredox-Cobaloxime Catalysis for Selective Oxidative Dehydrogenative [4+2] Annulation of Imidazo-Fused Heterocycles with Alkenes

A selective oxidative [4+2] annulation of alkenes with imidazo-fused heterocycles has been developed by using the synergistic combination of photoredox and cobaloxime catalysts. It allows facile access to various imidazole-fused polyaromatic scaffolds accompanied by H2 evolution. This protocol features high regioselectivity as well as a broad substrate scope. Detailed mechanistic studies indicate that twice the electron/H transfer processes facilitated by this catalytic system achieve the annulation π-extension of imidazo-fused heterocycles with alkenes.

Pd-catalyzed direct functionalization of glycals with cycloalkenones: application to the synthesis of chiral phenanthrenones

A palladium-catalyzed direct C-H functionalization of glycals with cycloalkenones is described and a series of C-2 functionalized glycals were synthesized efficiently with cyclic enones. The direct C-H functionalization of glycals with Pd(II) and subsequent insertion of cyclic enones via β-hydride elimination is the key to the synthesis of 2C-branched glycals. The synthetic utility of this methodology for chiral phenanthrenones has also been demonstrated by coupling the synthesized 2C-branched glycals with arynes via 4+2 cycloaddition followed by concomitant pyran ring opening.

Transition-metal-catalyzed C-H bond alkylation using olefins: recent advances and mechanistic aspects

Transition metal catalysis has contributed immensely to C-C bond formation reactions over the last few decades, and alkylation is no exception. The superiority of such methodologies over traditional alkylation is evident from minimal reaction steps, shorter reaction times, and atom economy while also allowing control over regio- and stereo-selectivity. In particular, hydrocarbonation of alkenes has grabbed increased attention due its fundamental ability to effectively and selectively synthesise a wide range of industrially and pharmaceutically relevant moieties. This review attempts to provide a scientific viewpoint and a systematic analysis of the recent developments in transition-metal-catalyzed alkylation of various C-H bonds using simple and activated olefins. The key features and mechanistic studies involved in these transformations are described briefly.

Synthesis of meta-(Indol-3-yl)phenols from Indoles and Cyclohexenone via Palladium(II)-Catalyzed Oxidative Heck Reaction and Dehydrogenative Aromatization in a One-Step Sequence

Facile construction of a meta-(indol-3-yl)phenol framework with a wide substrate scope (a total of 25 compounds) via a palladium(II)-catalyzed oxidative Heck reaction and dehydrogenative aromatization in a one-step sequence is reported. This methodology affords a novel route for the privileged structures that are challenging to access via a direct link between indole and phenol, in a highly efficient and atom-economical manner.

Electrooxidative double C-H/C-H coupling of phenols with 3-phenylbenzothiophenes: facile access to benzothiophene derivatives

An efficient electrooxidative double C-H/C-H coupling of phenols with 3-phenylbenzothiophene has been developed under external oxidant- and catalyst-free conditions. This strategy could enable the highly tunable access to benzothiophene derivatives and exhibited broad substrate generality under mild conditions. The reaction is likely to proceed via the cross-coupling of the p-methoxylphenol radical and the 3-phenylbenzothiophene radical cation.

Pd(II)-Catalyzed oxidative alkenylation of 4-hydroxycoumarin with maleimide via a C-H bond activation strategy

A Pd(ii)-catalyzed oxidative alkenylation of 4-hydroxycoumarins with maleimides for the synthesis of 4-hydroxy-3-maleimidecoumarins has been described. This methodology proceeds via C-H activation and C(sp2)-C(sp2) bond formation providing a series of alkenylated Heck-type products.

One-step synthesis of benzo[b]thiophenes by aryne reaction with alkynyl sulfides

An aryne reaction with alkynyl sulfides affording benzo[b]thiophenes is disclosed. A wide range of 3-substituted benzothiophenes were synthesized from easily available o-silylaryl triflates and alkynyl sulfides in a one-step intermolecular manner. The synthesis of diverse multisubstituted benzothiophene derivatives involving a pentacyclic compound was achieved by virtue of the good functional group tolerance and versatile C2 functionalizations.

Palladium-Catalyzed Regioselective Coupling Cyclohexenone into Indoles: Atom-Economic Synthesis of β-Indolyl Cyclohexenones and Derivatization Applications

Herein, we report a palladium-catalyzed dehydrogenative cross-coupling of indoles with cyclic enones to give β-indolyl cyclic enones under mild and neutral reaction conditions. The key to the success is to explore a mild condition, which ensures the indole C-H activation and subsequent syn β-hydride elimination through rapid enolization isomerization of Pd(II)-enolate while suppressing other undesired side reactions. Synthetic utility has also been demonstrated in the flexible transformation of the coupling products to meta-phenols and benzo[a]carbazoles.

Pd-Catalyzed Intermolecular Dehydrogenative Heck Reactions of Five-Membered Heteroarenes

The Pd-mediated cross-coupling of (hetero)arenes with alkenes may be an effective method for the formation of a C–C bond from two C–H bonds. Discovered by Fujiwara and co-workers in 1967, this reaction led to a number of reports that we firstly highlighted in 2011 (review with references till June 2010) and for which, we retained the name “dehydrogenative Heck reaction”. The topic, especially the reactions of five-membered heteroarenes, has been the subject of intensive research over the last ten years. The present review is limited to these dehydrogenative Heck reactions published since 2010, underlining the progress of the procedures.