Cobalt (II) catalysed allylation of 1,3-dicarbonyl compounds with allyl acetates

Cobalt-Catalyzed Allylic Alkylation at sp3-Carbon Centers

The rising demand and financial costs of noble transition metal catalysts have emphasized the need for sustainable catalytic approaches. Over the past few years, base-metal catalysts have emerged as ideal candidates to replace their noble-metal counterparts because of their abundance and easiness of handling. Despite the significant advancements achieved with precious transition metals, earth-abundant cobalt catalysts have emerged as efficient alternatives for allylic substitution reactions. In this review, allylic alkylations at sp3-carbon centers mediated by cobalt will be discussed, with a special focus on the mechanistic features, scope, and limitations.

Synthesis of Homoallylamines Enabled by Cobalt or Palladium Catalyzed Allylic Substitution of Azaarylmethylamines

Pd(OAc)2/Nixantphos or CoI2/Nixantphos catalyzed allylic substitutions with weakly acidic C(sp)3-H bonds of azaarylmethylamines are described. This method facilitates access to various kinds of heteroaryl rings containing homoallylamines (39 examples, 30-98% yields) with excellent functional group tolerance and diastereoselectivity. Compared with the Pd/Nixantphos complex, the Co/Nixantphos catalysis could obtain the cyclic products with good to excellent diastereoselectivities. Importantly, the CoI2/(R,R)-Me-Duphos catalyzed reactions exhibit moderate enantioselectivity. Additionally, the scalability of this transformation is successfully demonstrated.

Experimental and Computational Studies on Cobalt(I)-Catalyzed Regioselective Allylic Alkylation Reactions

Here, we report the development of cobalt(I)-catalyzed regioselective allylic alkylation reactions of tertiary allyl carbonates with 1,3-dicarbonyl compounds. A family of well-defined tetrahedral cobalt(I) complexes bearing commercially available bidentate bis(phosphine) ligands [(P,P)Co(PPh3 )Cl] are synthesized and explored as catalysts in allylic alkylation reactions. The catalyst [(dppp)Co(PPh3 )Cl] (dppp=1,3-Bis(diphenylphosphino)propane) enables the alkylation of a large variety of tertiary allyl carbonates with high yields and excellent regioselectivity for the branched product. Remarkably, this methodology is selective for the activation of tertiary allyl carbonates even in the presence of secondary allyl carbonates. This contrasts with the selectivity observed in cobalt-catalyzed allylic alkylations enabled by visible light photocatalysis. Mechanistic insights by means of experimental and computational investigations support a Co(I)/Co(III) catalytic cycle.

Recent advances in cobalt-catalyzed allylic functionalization

Unlike many other state-of-the-art transition-metal-catalyzed allylic substitutions, cobalt-catalyzed allylic substitution has received much less attention from synthetic chemists for a long time despite the fact that cobalt is an earth-abundant, low-cost and thus much more sustainable option as either a reagent or a catalyst in organic synthesis. Recently, there has been an upsurge in the use of cobalt catalysis in allylic functionalization reactions, including allylic substitution, nucleophilic allylation, and Heck-type allylic functionalization, to construct synthetically significant building blocks featuring a double bond available for diverse downstream synthetic manipulations. This review highlights the current development of cobalt catalysis in allylic functionalization with an in-depth discussion of the reaction scope and mechanistic insights.

Phenanthroline-A Versatile Ligand for Advanced Functional Polymeric Materials

The controlled incorporation of phenanthroline moieties into polymers is introduced, demonstrating their application as metal-ion complexing ligands for the construction of advanced macromolecular structures. Specifically, two phenanthroline-containing monomers based on acrylate and styrene functionalities, were synthesized. Each monomer was readily copolymerized with either N,N-dimethylacrylamide or styrene via nitroxide-mediated polymerization, resulting in narrowly distributed polar or non-polar copolymers. To demonstrate the versatility of the established polymer systems, the polar polymer was employed for transition metal induced single-chain nanoparticle formation, verified by diffusion-ordered NMR and UV/Vis spectroscopy. Furthermore, the non-polar polymer allows facile incorporation of lanthanide ions, creating luminescent metallo-polymers, in-depth characterized by advanced photophysical experiments and 2D NMR measurements.

Regio- and Enantioselective Rhodium-Catalyzed Addition of 1,3-Diketones to Allenes: Construction of Asymmetric Tertiary and Quaternary All Carbon Centers

An unprecedented highly regio- and enantioselective rhodium-catalyzed addition of 1,3-diketones to terminal and 1,1-disubstituted allenes furnishing asymmetric tertiary and quaternary all-carbon centers is reported. By applying a Rh^I /phosphoramidite/TFA catalytic system under mild conditions, the desired chiral branched α-allylated 1,3-diketones could be obtained in good to excellent yields, with perfect regioselectivity and in high enantioselectivity. The reaction shows a broad functional-group tolerance on both reaction partners highlighting its synthetic potential.

Tandem Rh-catalysis: decarboxylative β-keto acid and alkyne cross-coupling

Herein, we describe a regioselective Rh-catalyzed decarboxylative cross-coupling of β-keto acids and alkynes to access branched γ,δ-unsaturated ketones. Rh-hydride catalysis enables the isomerization of an alkyne to generate a metal-allyl species that can undergo carbon-carbon bond formation. Ketones are generated under mild conditions, without the need for base or activated electrophiles.

Regioselective Rhodium-Catalyzed Addition of 1,3-Dicarbonyl Compounds to Terminal Alkynes

A new method for the rhodium-catalyzed regioselective C-C bond formation using terminal alkynes and 1,3-dicarbonyl compounds to achieve valuable branched α-allylated 1,3-dicarbonyl products is reported. With a Rh(I)/DPEphos/p-CF3-benzoic acid as the catalyst system, the desired products can be obtained in good to excellent yields and with perfect regioselectivity. A broad range of functional groups were tolerated, and first experimental insights of a plausible reaction mechanism were obtained.

Palladium-Catalyzed DYKAT of Butadiene Monoepoxide: Enantioselective Total Synthesis of (+)-DMDP, (−)-Bulgecinine, and (+)-Broussonetine G

Palladium catalyzed asymmetric allylic alkylation reaction of an amine with two equivalents of butadiene monoxide allows for the expedient synthesis of trans- and cis-2,5-dihydropyrroles. The versatility of these chiral synthons towards the synthesis of a wide variety of iminosugar natural products was demonstrated with the short and high yielding asymmetric syntheses of (+)-DMDP, and (-)-bulgecinine. In addition, the first total synthesis of (+)-broussonetine G, a potent glycosidase inhibitor, is described along with the assignment of its relative and absolute stereochemical configuration.

Rhodium-catalyzed asymmetric ring opening reactions of oxabicyclic alkenes: catalyst and substrate studies leading to a mechanistic working model

Catalyst and substrate studies have been performed on the rhodium-catalyzed asymmetric ring opening reaction. A working model is advanced that involves oxidative insertion with retention to form an organorhodium intermediate that then undergoes nucleophilic attack with inversion. Kinetic and competition experiments have uncovered evidence for a proton transfer step in the catalytic cycle that may activate both the allylrhodium intermediate and the nucleophile. We have also conducted experiments designed to understand which properties of the PPF-P(t)Bu(2) ligand contribute to the high reactivities and enantioselectivities.

Direct, Stereoselective Substitution in [Rh(CO)2Cl]2-Catalyzed Allylic Alkylations of Unsymmetrical Substrates

[Rh(CO)(2)Cl](2) has been found to possess the unusual property of catalyzing allylic alkylations of unsymmetrical allylic carbonates with high levels of regioselectivity to provide products arising from substitution at the carbon atom bearing the leaving group, irrespective of the structure of the starting carbonate. The substitution reaction occurs with retention of stereochemistry at the reacting center, and the carbon-carbon double-bond stereochemistry of primary (Z)-allylic carbonates is maintained. [reaction: see text]