Formation of a carbonyl group ortho to a biaryl structure or a 6H-dibenzopyran by a palladium/norbornene-catalyzed ordered reaction sequence

Synthesis of fluorenyl alcohols via cooperative palladium/norbornene catalysis

Herein, we report a novel catalytic synthesis of substituted 9H-fluoren-9-ols starting from aryl iodides and secondary ortho-bromobenzyl alcohols in the presence of palladium/norbornene as a catalytic system. The present protocol exhibits high functional group tolerance, mild reaction conditions and moderate to good yields. This transformation is based on two sequential pathways: (i) Pd(ii)-mediated oxidation of the secondary alcohol to the corresponding ketone and (ii) Pd(0)/norbornene-catalyzed reaction of the in situ generated ortho-bromoacetophenone with the aryl iodide.

Chemoselective Borono-Catellani Arylation for Unsymmetrical Biaryls Synthesis

Reported is the borono-Catellani arylation process for unsymmetrical biaryls synthesis, utilizing the readily available pinacol ester of arylboronic acids, aryl bromides, and olefins as the reactants. The distinct reactivity of arylboronic ester and aryl bromides secures the excellent chemoselectivity in the pivotal arylation step. The reaction is enabled by the cooperative catalysis of Pd(OAc)₂ and the NBE derivative N⁷, with molecular oxygen as the terminal oxidant.

C-H alkylation reactions of indoles mediated by Pd(ii) and norbornene: applications and recent developments

The Catellani reaction enables an ortho-C-H activation based on oxidative addition of Pd(0) and an intermediary carbopalladation of norbornene. Among its variants, the recently developed C2-selective alkylation of indoles is particular as it employs Pd(ii) as the source of palladium. This review describes the mechanistic background of this transformation. Applications in total synthesis and in the synthesis of biologically relevant molecules are illustrated and further developments of the method are discussed.

The vinylogous Catellani reaction: a combined computational and experimental study

In the presence of 5 mol% Pd(OAc)₂, 1 equiv. of norbornene, and K₂CO₃, the reaction of 4-iodo-2-quinolones with tertiary o-bromobenzylic alcohols produced the desired benzopyran-fused 2-quinolones in moderate to high yields.

In the presence of 5 mol% Pd(OAc)₂, 1 equiv. of norbornene, and K₂CO₃, the reaction of 4-iodo-2-quinolones with tertiary o-bromobenzylic alcohols produced the desired benzopyran-fused 2-quinolones in moderate to high yields. A Catellani-type mechanism involving vinylic C–H cleavage is proposed based on the results of control experiments and density functional theory calculations.

Pd/Norbornene: A Winning Combination for Selective Aromatic Functionalization via C-H Bond Activation

Direct C-H bond activation is an important reaction in synthetic organic chemistry. This methodology has the potential to simplify reactions by avoiding the use of prefunctionalized reagents. However, selectivity, especially site selectivity, remains challenging. Sequential reactions, in which different molecules or groups are combined in an ordered sequence, represent a powerful tool for the construction of complex molecules in a single operation. We have discovered and developed a synthetic methodology that combines selective C-H bond activation with sequential reactions. This procedure, which is now known as the "Catellani reaction", enables the selective functionalization of both the ortho and ipso positions of aryl halides. The desired molecules are obtained with high selectivity from a pool of simple precursors. These molecules are assembled under the control of a palladacycle, which is formed through the joint action of a metal (Pd) and an olefin such as norbornene. These two species act cooperatively with an aryl halide to construct the palladacycle, which is formed through ortho-C-H activation of the original aryl halide. The resulting complex acts as a scaffold to direct the reaction (via Pd(IV)) of other species, such as alkyl or aryl halides and amination or acylation agents, toward the sp(2) C-Pd bond. At the end of this process, because of steric hindrance, the scaffold is dismantled by norbornene extrusion. Pd(0) is cleaved from the organic product through C-C, C-H, C-N, C-O, or C-B coupling, in agreement with the well-known reactivity of aryl-Pd complexes. The cycle involves Pd(0), Pd(II), and Pd(IV) species. In particular, our discovery relates to alkylation and arylation reactions. Recently, remarkable progress has been made in the following areas: (a) the installation of an amino or an acyl group at the ortho position of aryl halides, (b) the formation of a C-B bond at the ipso position, (c) the achievement of meta-C-H bond activation of aryl rings bearing a chelating directing group by Pd(II)/Pd(IV)/norbornene catalysis, and (d) the activation of N-H and C-H bonds in sequence for indole 2-alkylation. In this Account, we explain the main features of this methodology, describe its synthetic potential, and illustrate some remarkable progress that has been made, emphasizing the most recent developments and applications in total synthesis.