Synergistic catalysis, a type of plural catalysis which utilizes at least two different catalysts to enable a reaction between two separately activated substrates, has unlocked a plethora of previously unattainable transformations and novel chemical reactivity. Despite the appreciable utility of synergistic catalysis, specific examples involving two transition metals have been limited, as ensuring a judicious choice of reaction parameters to prevent deactivation of catalysts, undesirable monocatalytic event(s) leading to side products, or premature termination and other potentially troublesome outcomes present a formidable challenge. Excluding those driven by photocatalytic mechanisms, this review will highlight the reported examples of reactions that make use of two simultaneous catalytic cycles driven by two transition metal catalysts.

Extensive effort has been expended to utilize π-allyl palladium-complexes as electrophilic allyl donor intermediates in cooperative dual catalysis, but their counter anions such as carboxylates or alkoxides are almost always discarded as waste. We have developed a cooperative Pd(0)/Rh(II) dual catalysis system that utilizes both the electrophilic allyl and nucleophilic counter anion functionalities inherent in the starting allylic substrates. In this cooperative catalysis, redox compatible Pd(0) and Rh(II) catalysts selectively activate allylic substrates and N-sulfonyl-1,2,3-triazoles to generate π-allyl Pd(II)-complexes and 1,3-ambivalent equivalent aimino Rh(II)-carbenoid intermediates, respectively. The counter anion of the π-allyl Pd(II)-complex acts as a nucleophile transferring to the electrophilic carbenic carbon to form Pd/Rh-associated zwitterionic intermediates, in which the cationic palladium species may coordinate with both counter anion and imine nitrogen in the same plane establishing the (Z)-geometry of the products.

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Described herein is an organoboranecatalysed consecutive borylative reduction of quinolines and isoquinolines to furnish tetrahydro(iso) quinolines bearing a C(sp 3 )À B bond β to the nitrogen atom. The installed CÀ B bond is oxidatively transformed to the hydroxy group in one pot. The present double hydroboration is proposed to proceed via a stepwise ionic mechanism involving a boronium ion. The stereo-outcome was found to be dependent on the position (C2 vs C4) of the substituents in quinolines.

The first example of a highly regio- and stereoselective catalytic method for the three-component one-pot synthesis of highly functionalized α-vinylated γ-oxo-β-amino esters is disclosed. In this catalytic triad, the Cu(I)-catalyst selectively catalyzes the cycloaddition of the 1-alkyne and sulfonyl azide first resulting in the corresponding 1-sulfonyl-1,2,3-triazole. An α-imino Rh(II)-carbene is generated from an open-chain α-imino diazo of the triazole, and this species reacts with γ-hydroxy α,β-unsaturated esters to form allylic (Z)-amino vinyl ethers. Rapid deconjugative [3,3]-sigmatropic rearrangement affords the α-vinyl γ-oxo-β-amino esters in high yields with high levels of diastereoselectivity.

A novel, one-pot route for the synthesis of nonaromatic ring-fused 1,4-oxazepines and 1,4-oxazines has been developed. The reaction features a sequential rhodium(II)-catalyzed reaction of N-sulfonyl-1,2,3-triazoles with glycidols, followed by a regioselective Lewis acid Mg(OBu)-catalyzed intramolecular ring-opening reaction. It has been found that the regioselectivity in the epoxide ring-opening was largely determined by the substituents on the glycidols. Thus, substituted glycidols (R ≠ H) afforded seven-membered oxazepine derivatives selectively, while unsubstituted glycidols (R = H) afforded six-membered oxazine derivatives. Plausible reaction pathways are elucidated and supported by experiments with several glycidols bearing different substituents around the epoxide functionality.

A rhodium(ii)-catalyzed coupling of 1-sulfonyl-1,2,3-triazoles, prepared from 1-alkynes and sulfonyl azides, with Morita-Baylis-Hillman (MBH) adducts afforded highly functionalized α-methylene-δ-oxo-γ-amino esters in excellent yields with broad functional group tolerance. This transformation can also be successfully accomplished as a multicomponent all-in-one-pot reaction of 1-alkynes, sulfonyl azides and MBH adducts in the presence of Cu(i) and Rh(ii) catalysts.

A new catalytic reaction in which all the atoms of a formamide are incorporated into the product through a formal stereoselective 1,2-insertion of rhodium(II) azavinyl carbenes, generated in situ from readily available N-sulfonylated 1,2,3-triazoles, into the C═O bond of DMF and other N,N-disubstituted formamides to afford cis-diamino enones is described.