Catalysis by defined transition-metal complexes has captivated the attention of the scientific community over the last decades. The well-documented utility of Rh(III) complexes in C−H activation reactions have enabled the development of a plethora of new catalytic methods. High-valent transition-metal species in C−H activation reactions were first predicted in palladium-based transformations. From those early studies, it was apparent that differences in reactivity and selectivity could be expected. By analogy, higher valent Rh(V) complexes could represent a new approach in C−H activation reactions and offer different opportunities to improve and broaden the current state-of-the-art in the field.

A spiroketal bisphosphine (SKP) derived chiral digold complex is identified as a powerful catalyst for the highly diastereo- and enantioselective synthesis of spirocyclopropyloxindoles from diazooxindoles and a broad range of alkenes, including both cis and trans 1,2-disubstituted alkenes.

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The first Cp*Rh(III) -catalyzed arylation of unactivated C(sp(3) )-H bonds is presented. The unactivated primary C(sp(3) )-H bond of 2-alkylpyridines can be activated by Rh(III) and further reacts with triarylboroxines to efficiently build new C(sp(3) )-aryl bonds. The methodology also provides a facile and efficient synthesis of unsymmetrical triarylmethanes by Rh(III) -catalyzed C(sp(3) )-H arylation of diarylmethanes.

The design of chiral ligands plays a central role in the development of chiral catalysts for asymmetric reactions, in which the right combination of a sterically well-defined scaffold with a chelating moiety can lead to excellent enantioselective control in the catalysis.[1] From this point of view, spirobackbones (Scheme 1) have been recognized as one of the privileged structures for the construction of chiral ligands [2] ever since the pioneering work by Chan et al. (SpirOP), Sasai and co-workers, and Zhou and co-workers (SDP).[3] In contrast, van Leeuwen and co-workers reported the development of the bisphosphine ligands SPANphos which have an interesting spiro-2,2'-bis(chroman) backbone and their transition-metal complexes have been studied in catalysis.[4] Despite the success of their rhodium(I) complexes in the catalysis of methanol carbonylation,[4c] the application of spiro-2,2-bis(chroman)-based chiral ligands in asymmetric catalysis still remains relatively unexplored. [4e,g, 5] Very recently, we developed a catalytic asymmetric synthesis of aromatic spiroketals by the tandem hydrogenation and spiroketalization of a,a'-bis(2-hydroxyarylidene)ketones [6a] using Ir/SpinPHOX as the catalyst, [6] and it provides a facile and practical synthesis of a new type of enantiopure analogoue to SPANphos, namely SKP (1). In our ongoing endeavor towards seeking new spirochiral ligands for asymmetric catalysis, we communicate herein our preliminary results on the synthesis of one type of chiral bisphospine ligand having an aromatic spiroketal motif (1; SKP) and their application in palladium-catalyzed enantioselective allylic amination of racemic Morita-Baylis-Hillman (MBH) adducts [7] with aromatic amines. The developed methodology has provided a facile and efficient synthesis of optically active b-lactam derivatives, [8] including the chiral drug Ezetimibe which is used to treat high cholesterol. [9] As shown in Scheme 2, synthesis of the enantiopure spiro-2,2'-bis(chroman)-based bishosphine ligands (R,R,R)-1 is quite simple and straightforward from readily available a,a'-bis(2-hydroxy-3-bromophenylidene)ketone (2) by using our previously published procedure.[6a] The key intermediate, the 3-bromo-substituted aromatic spiroketal (R,R,R)-3 was treated with nBuLi and the resulting lithium salt was reacted with Ar 2 PCl in THF to afford the corresponding enantiopure spiroketal-based bisphosphine ligands (R,R,R)-1 a-f in moderate to good yields (40-80 %) on gram scale.Optically active a-alkylidene-b-arylamino carbonyl compounds represent one type of valuable building blocks with wide applications in the synthesis of medicinally relevant molecules and natural products, [10] but these building blocks are not readily accessible using direct asymmetric aza-MBH reactions because of the electron-rich nature of the corresponding N-aromatic imines. [7,11] In contrast, the enantioselective, metal-catalyzed allylic amination is a useful method for the preparation of enantiomerically enriched allylic amines.[12] Despite the suc...

A comparative study on the catalytic activity of different group 9 [Cp*M(III)] complexes in the formal [4 + 2] cycloaddition of arenes with rarely explored free imines and dioxazolones for the construction of multisubstituted quinazolines is reported herein. This investigation revealed that the cobalt catalyst is uniquely suited to this transformation due to its strong Lewis acidity and high sensitivity to steric hindrance.

A bicyclic olefin was discovered as a cocatalyst in a Cp*Rh(III)-catalyzed C-H bond amidation proceeding by an intramolecular amide transfer in N-phenoxyacetamide derivatives. Combining experimental and theoretical studies, we propose that the olefin promotes a Rh(III) intermediate to undergo oxidative addition into the O-N bond to form a Rh(V) nitrenoid species and subsequently direct the nitrenoid to add to the ortho position. The amide directing group plays a dual role as a cleavable coordinating moiety as well as an essential coupling partner for the C-H amidation. This methodology was successfully applied to the late-stage diversification of natural products and a marketed drug under mild conditions.

A combination of Cp*Rh -catalyzed C-H activation and Wagner-Meerwein-type rearrangement was successfully achieved for the first time. Thus, bridged polycyclic molecules that are not readily accessible by other means were accessed under mild conditions with high efficiency (as low as 0.5 mol % Rh catalyst) in the coupling of N-phenoxyacetamide with 7-azabenzonorbornadiene.