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

Abstract

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.

Palladium-Catalyzed Dehydrogenative C-2 Alkenylation of 5-Arylimidazoles and Related Azoles with Styrenes

“…The unexpected formation of compound 4 can be explained by admitting that the carbopalladation of styrene by the Pd-imidazole complex (resulting from the activation of the heteroaromatic C2-H bond) occurred with not complete regioselectivity. [11] An even worse result was observed when 1a and 2a were reacted using the Joo protocol, [38] i.e. in the presence of 10 mol% Pd(OAc)2 and 2.0 equiv of KOAc in DMA under an oxygen atmosphere.…”

“…These unsatisfactory results prompted us to search for alternative reaction conditions. Considering that classical Fujiwara-Moritani protocols require the use of simple carboxylic acid (such as acetic acid) as the reaction solvent, [3,13] and that many of the reported procedures for the dehydrogenative alkenylation of azoles have been carried out in acidic solvents, [4,11] we decided to start a screening of the reaction conditions using a carboxylic acid as the solvent and examining the influence of the nature of the solvent, the oxidant, and the palladium pre-catalyst on the reaction outcome.…”

“…Transition metal-catalyzed carbon-carbon bond-forming reactions that occur by breaking of carbon-hydrogen bonds are attracting increasing interest in modern synthetic organic chemistry since this approach does not require any pre-activation of the starting materials. [1][2][3][4][5][6][7][8][9][10][11] When compared with conventional cross-coupling methodologies that require the use of organic halides and/or preformed organometallic reagents this strategy, known as cross dehydrogenative coupling (CDC), allows to obtain a high degree of atom economy and structural complexity in the target molecule, while ensuring high chemoselectivity. In addition, unlike traditional cross-couplings, the possibility of avoiding the use of metals and halogens in stoichiometric quantities reduces the production of inorganic waste.…”

Pd-catalyzed Intermolecular Dehydrogenative Heck Reactions of Six-membered Heteroarenes

“…We earlier reviewed the corresponding literature with references until June 2010 [4] using the term "Dehydrogenative Heck Reactions" (DHRs), initially proposed by Stoltz [5], to name such reactions which eliminate two H atoms and occur via an arylpalladium II intermediate. Recently, we reviewed the DHRs of five membered heteroarenes reported over the last ten years [6]. We now highlight the DHRs of six membered heteroarenes published during the same period [7].…”

Combustion-Synthesized Porous CuO-CeO2-SiO2 Composites as Solid Catalysts for the Alkenylation of C(sp3)-H Bonds Adjacent to a Heteroatom via Cross-Dehydrogenative Coupling

“…In recent years, cross-dehydrogenative coupling (CDC) to directly build a C-C bond from two simple C-H bonds has emerged as an attractive goal in organic synthesis [1,2]. Offering great benefits including improving atom economy, step efficiency, and reducing cost and waste, the CDC reaction is a more efficient synthetic protocol to access product molecules compared to traditional cross-couplings, which often require the use of prefunctionalized halides and organometallic reagents [1,[3][4][5].…”