A convenient three‐component coupling reaction for the construction of conjugated enynes using rhodium catalysis is reported. Dimerization of a monosubstituted alkyne followed by trapping of the vinyl metal intermediate with an electron‐deficient alkene, such as methyl vinyl ketone, provided moderate to good yields of these enynes. The use of the hindered electron‐rich tris(ortho‐tolyl)phosphine as a ligand for the rhodium catalyst provided the best conversions to these complex products.
A synthesis of pyrido[2,1‐a]isoindoles is reported by the rhodium‐catalyzed direct oxidative C H acylation of 2‐aryl pyridines with terminal alkynes. The desired products were obtained in moderate to excellent yields. This is an efficient and clean method to construct C C/C N bonds in one step. In addition, the effective rhodium(III) catalyst was isolated and characterized by X‐ray crystallography.
The synthesis of chiral bidentate bisphosphonite ligands based on the TADDOL motif from readily available starting materials has been developed. Taking advantage of the modular nature of the building blocks, a diverse ligand library has been prepared. Their catalytic potential has been evaluated in the asymmetric hydroformylation of styrene and derivatives. These catalysts showed high activity and provided the aldehydes in high enantiomeric purity.
A method for using amine–borane complexes directly in palladium catalyzed borylation has been developed. The reaction proceeds through the sequential formation of a boronium species followed by deprotonation leading to the aminoborane. This reagent is then directly used in the borylation process leading, after work‐up, to various boronic acid derivatives. The reaction was applied to (hetero)aryl triflates, iodides, bromides and chlorides.
An efficient strategy for the regioselective ortho‐acylation of azoxybenzenes with various aldehydes in the presence of palladium catalysts has been developed and furnishes good to excellent yields. The reaction proceeds smoothly and can tolerate a variety of functional groups.
By using a nitrone as the oxidizing directing group, a mild, practical and efficient rhodium(III)‐catalyzed C H functionalization for the synthesis of indole derivatives has been developed. This reaction obviates the need for an external oxidant and shows good functional group tolerance. The employment of a sterically hindered Mes group on the carbon center of the nitrone is crucial to produce indoles in high yield.
A sequential one‐pot synthesis of Michael adducts of aroylmethylidenemalonates with activated aromatics is described. The method involves treatment of trans‐2‐aryl‐3‐nitro‐cyclopropane‐1,1‐dicarboxylates with boron trifluoride etherate to form aroylmethylidenemalonates in situ and then addition of activated aromatics such as indoles, carbazole, pyrrole, thiophenes, methoxybenzenes and benzodioxole followed by a catalytic amount of indium(III) triflate to the same reaction vessel. To prove the synthetic potential of the resulting Michael adducts, one of the adducts was transformed into a pharmaceutically interesting dihydropyridazinone derivative.
This review describes recent progress made in the rapidly developing field of C H bond activation, in particular for syntheses of biaryls. The catalysts presented here provide convenient strategies for the direct arylation of arenes, via single or double C H bond activation, leading to inter‐, and intramolecular carbon‐carbon bond formation. The literature from mid‐2009 to December 2013 has been discussed.
Sequential copper‐catalyzed [3+2] cycloaddition, rhodium‐catalyzed O H insertion, intramolecular 1,8‐addition, and rearrangement starting from 1‐alkynes, N‐sulfonyl azides, and tropolones is demonstrated for the synthesis of the 2‐functionalized aminotropones in one pot. These results indicate that sequential functionalization of O H and C(sp2) O bonds smoothly occurs in the C(sp2) O H bonds of tropolone
