The intramolecular Pd­(II)-catalyzed alkenylation of aryl homoallyl ethers constitutes a mild, versatile, and efficient procedure for the synthesis of highly and diversely substituted chromanes and 2H-chromenes. The use of p-TsOH as an additive allows more efficient reactions that could be carried out a room temperature in most cases. The procedure has a wide scope, allowing the synthesis of alkylidenechromanes and 2H-chromenes substituted at C-2 or C-3 of the chromene moiety, thus accessing relevant flavenes and isoflavenes, and even coumarins, in high yields (59 to 91%, 32 examples).

Palladium-catalyzed dehydrogenative coupling is an efficient synthetic strategy for the construction of quinoline scaffolds, a privileged structure and prevalent motif in many natural and biologically active products, in particular in marine alkaloids. Thus, quinolines and 1,2-dihydroquinolines can be selectively obtained in moderate-to-good yields via intramolecular C–H alkenylation reactions, by choosing the reaction conditions. This methodology provides a direct method for the construction of this type of quinoline through an efficient and atom economical procedure, and constitutes significant advance over the existing procedures that require preactivated reaction partners.

Site-selective installation of C−Me bonds remains a powerful and sought-after tool to alter the chemical and pharmacological properties of a molecule. Direct C−H functionalization provides an attractive means of achieving this transformation. Such protocols, however, typically utilize harsh conditions and hazardous methylating agents with poor applicability toward late-stage functionalization. Furthermore, highly monoselective methylation protocols remain scarce. Herein, we report an efficient monoselective, directed ortho-methylation of arenes using N,N,N-trimethylanilinium salts as noncarcinogenic, bench-stable methylating agents. We extend this protocol to d 3 -methylation in addition to the late-stage functionalization of pharmaceutically active compounds. Detailed kinetic studies indicate the rate-limiting in situ formation of MeI is integral to the observed reactivity.

Recent developments in Pd(0)- and Pd(ii)-catalysed alkenylation reactions for the synthesis of quinolines focusing on mechanistic understanding.

The use of earth-abundant first-row transition metals, such as cobalt, in C–H activation reactions for the construction and functionalization of a wide variety of structures has become a central topic in synthetic chemistry over the last few years. In this context, the emergence of cobalt catalysts bearing pentamethylcyclopentadienyl ligands (Cp*) has had a major impact on the development of synthetic methodologies. Cp*Co(III) complexes have been proven to possess unique reactivity compared, for example, to their Rh(III) counterparts, obtaining improved chemo- or regioselectivities, as well as yielding new reactivities. This perspective is focused on recent advances on the alkylation and alkenylation reactions of (hetero)arenes with alkenes and alkynes under Cp*Co(III) catalysis.

Six- and seven-membered ring-fused, functionalized cyclopentadienes can be obtained in moderate to excellent yields by a cascade process entailing the Au­(I)-catalyzed propargyl Claisen rearrangement/Nazarov cyclization of propargyl vinyl ethers, the hetero-Diels–Alder reaction with dialkylazodicarboxylates, and the spontaneous conversion of cycloaddition products into cyclopentadienes by a highly regioselective cleavage of a C–N bond. Depending on the treatment of the crude reaction mixtures, two types of products can be obtained: cyclopentadienes with pendant hydrazine and aldehyde moieties that intramolecularly react to form hemiaminals are obtained in 43–52% overall yields when the crude reaction mixtures are left over K2CO3 in a DCM solution. Instead, by reducing in situ the aldehyde group just after addition of the heterodienophile, the regioselective C–N bond cleavage generates the corresponding cyclopentadienes bearing a hydrazine and an alcohol appendage in excellent yields (66–82%) over four steps, all in one pot. Two examples from the latter class of compounds were also converted into ring-fused, functionalized cyclopentadienes, bearing a protected amino group, by the selective N–N cleavage of the hydrazine moiety.

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The first example of Cp*Co­(III)-catalyzed intramolecular hydroarylation of allyl aryl ethers using an amide directing group for the preparation of 3,3-disubstituted dihydrobenzofurans in high yields is described. The reaction of the unactivated alkene is completely selective for the formation of the quaternary center, allowing different substitution patterns on the aromatic ring and the alkene. The cyclization can also be extended to the formation of six-membered rings and to N-homoallylindoles.