Metalloradical Catalysis Research Articles

Synthesis of chiral N-phosphoryl aziridines through enantioselective aziridination of alkenes with phosphoryl azide via Co(II)-based metalloradical catalysis.

The Co(II) complex of a new D2-symmetric chiral porphyrin 3,5-DiMes-QingPhyrin, [Co(P6)], can catalyze asymmetric aziridination of alkenes with bis(2,2,2-trichloroethyl)phosphoryl azide (TcepN3) as a nitrene source. This new Co(II)-based metalloradical aziridination is suitable for different aromatic olefins, producing the corresponding N-phosphorylaziridines in good to excellent yields (up to 99%) with moderate to high enantioselectivities (up to 85% ee). In addition to mild reaction conditions and generation of N2 as the only byproduct, this new metalloradical catalytic system is highlighted with a practical protocol that operates under neutral and non-oxidative conditions.

Chemoselective amination of propargylic C(sp³)-H bonds by cobalt(II)-based metalloradical catalysis.

Highly chemoselective intramolecular amination of propargylic C(sp(3))-H bonds has been demonstrated for N-bishomopropargylic sulfamoyl azides through cobalt(II)-based metalloradical catalysis. Supported by D(2h)-symmetric amidoporphyrin ligand 3,5-Di(t)Bu-IbuPhyrin, the cobalt(II)-catalyzed C-H amination proceeds effectively under neutral and nonoxidative conditions without the need of any additives, and generates N2 as the only byproduct. The metalloradical amination is suitable for both secondary and tertiary propargylic C-H substrates with an unusually high degree of functional-group tolerance, thus providing a direct method for high-yielding synthesis of functionalized propargylamine derivatives.

Chemoselective Amination of Propargylic C(sp3)H Bonds by Cobalt(II)‐Based Metalloradical Catalysis

AbstractHighly chemoselective intramolecular amination of propargylic C(sp3)H bonds has been demonstrated for N‐bishomopropargylic sulfamoyl azides through cobalt(II)‐based metalloradical catalysis. Supported by D2h‐symmetric amidoporphyrin ligand 3,5‐DitBu‐IbuPhyrin, the cobalt(II)‐catalyzed CH amination proceeds effectively under neutral and nonoxidative conditions without the need of any additives, and generates N2 as the only byproduct. The metalloradical amination is suitable for both secondary and tertiary propargylic CH substrates with an unusually high degree of functional‐group tolerance, thus providing a direct method for high‐yielding synthesis of functionalized propargylamine derivatives.

Stereoselective Intramolecular Cyclopropanation of α-Diazoacetates via Co(II)-Based Metalloradical Catalysis.

Co(II) complexes of D2-symmetric chiral porphyrins have been proven to be effective metalloradical catalysts for the asymmetric intramolecular cyclopropanation of allyl α-diazoacetates. 4-(Dimethylamino)pyridine (DMAP), through positive trans effect, plays an important role in the enhancement of the asymmetric induction for the intramolecular cyclopropanation process. This metalloradical catalytic system is suitable for cyclopropanation of allyl α-diazoacetates with varied functional groups and substitution patterns, producing bicyclic products with complete diastereocontrol and good enantiocontrol.

Selective radical amination of aldehydic C(sp2)–H bonds with fluoroaryl azides via Co(ii)-based metalloradical catalysis: synthesis of N-fluoroaryl amides from aldehydes under neutral and nonoxidative conditions

The Co(II) complex of the D2h-symmetric amidoporphyrin 3,5-Di t Bu-IbuPhyrin, [Co(P1)], has proven to be an effective metalloradical catalyst for intermolecular amination of C(sp2)-H bonds of aldehydes with fluoroaryl azides. The [Co(P1)]-catalyzed process can employ aldehydes as the limiting reagents and operate under neutral and non-oxidative conditions, generating nitrogen gas as the only byproduct. The metalloradical aldehydic C-H amination is suitable for different combinations of aldehydes and fluoroaryl azides, producing the corresponding N-fluoroaryl amides in good to excellent yields. A series of mechanistic studies support a stepwise radical mechanism for the Co(II)-catalyzed intermolecular C-H amination.

ChemInform Abstract: Stereoselective Radical Amination of Electron‐Deficient C(sp3)—H Bonds by Co(II)‐Based Metalloradical Catalysis: Direct Synthesis of α‐Amino Acid Derivatives via α‐C—H Amination.

AbstractTreatment of sulfamoyl azides with the Co complex COP allows an efficient, regio‐ and stereoselective access to cyclic sulfamides.

Stereoselective radical amination of electron-deficient C(sp3)-H bonds by Co(II)-based metalloradical catalysis: direct synthesis of α-amino acid derivatives via α-C-H amination.

The cobalt(II) complex of 3,5-Di(t)Bu-IbuPhyrin, [Co(P1)], is an effective catalyst for intramolecular amination of electron-deficient C-H bonds, including those adjacent to electron-withdrawing CO(2)R, C(O)NR(2), C(O)R, and CN groups, in excellent yields with high regio- and stereoselectivity. The [Co(P1)]-catalyzed amination system provides a direct method for the synthesis of α-amino acid derivatives from the corresponding carboxylate precursors.

ChemInform Abstract: Highly Asymmetric Intramolecular Cyclopropanation of Acceptor‐Substituted Diazoacetates by Co(II)‐Based Metalloradical Catalysis: Iterative Approach for Development of New‐Generation Catalysts.

AbstractA newly synthesized cobalt(II)‐catalyst is effectively used in the asymmetric intramolecular cyclopropanation of various α‐acceptor‐substituted diazoacetates providing oxabicyclo[3.1.0]hexan‐2‐one derivatives with high diastereo‐ and enantioselectivity.

Highly Asymmetric Intramolecular Cyclopropanation of Acceptor-Substituted Diazoacetates by Co(II)-Based Metalloradical Catalysis: Iterative Approach for Development of New-Generation Catalysts

3,5-Di(t)Bu-QingPhyrin, a new D(2)-symmetric chiral porphyrin derived from a chiral cyclopropanecarboxamide containing two contiguous stereocenters, has been developed using an iterative approach based on Co(II)-catalyzed asymmetric cyclopropanation of alkenes. The Co(II) complex of 3,5-Di(t)Bu-QingPhyrin, [Co(P2)], has proved to be a general and effective catalyst for asymmetric intramolecular cyclopropanation of various allylic diazoacetates (especially including those with α-acceptor substituents) in high yields with excellent stereoselectivities. The [Co(P2)]-based intramolecular metalloradical cyclopropanation provides convenient access to densely functionalized 3-oxabicyclo[3.1.0]hexan-2-one derivatives bearing three contiguous quaternary and tertiary chiral centers with high enantiomeric purity.

ChemInform Abstract: Enantioselective Cyclopropenation of Alkynes with Acceptor/Acceptor‐Substituted Diazo Reagents via Co(II)‐Based Metalloradical Catalysis.

AbstractThe new Co complex (I) efficiently promotes the asymmetric cyclopropenation of various aromatic and conjugated alkynes with diazo compounds.

Enantioselective Cyclopropenation of Alkynes

The cobalt(II) complex of new D2-symmetric chiral porphyrin 3,5-DiMes-ChenPhyrin, [Co(P2)], has been shown to be a highly effective chiral metalloradical catalyst for enantioselective cyclopropenation of alkynes with acceptor/acceptor-substituted diazo reagents such as α-cyanodiazoacetamides and α-cyanodiazoacetates. The [Co(P2)]-mediated metalloradical cyclopropenation is suitable to a wide range of terminal aromatic and related conjugated alkynes with varied steric and electronic properties, providing the corresponding tri-substituted cyclopropenes in high yields with excellent enantiocontrol of the all-carbon quaternary stereogenic centers. In addition to mild reaction conditions, the Co(II)-based metalloradical catalysis for cyclopropenation features a high degree of functional group tolerance.

Enantioselective Cyclopropenation of Alkynes with Acceptor/Acceptor-Substituted Diazo Reagents via Co(II)-Based Metalloradical Catalysis

The cobalt(II) complex of a new D(2)-symmetric chiral porphyrin 3,5-diMes-ChenPhyrin, [Co(P2)], has been shown to be a highly effective chiral metalloradical catalyst for enantioselective cyclopropenation of alkynes with acceptor/acceptor-substituted diazo reagents, such as α-cyanodiazoacetamides and α-cyanodiazoacetates. The [Co(P2)]-mediated metalloradical cyclopropenation is suitable to a wide range of terminal aromatic and related conjugated alkynes with varied steric and electronic properties, providing the corresponding trisubstituted cyclopropenes in high yields with excellent enantiocontrol of the all-carbon quaternary stereogenic centers. In addition to mild reaction conditions, the Co(II)-based metalloradical catalysis for cyclopropenation features a high degree of functional group tolerance.

Chemoselective intramolecular allylic C–H amination versus CC aziridination through Co(ii)-based metalloradical catalysis

Excellent chemoselectivity for intramolecular allylic C–H aminationversus CC aziridination was achieved through Co(II)-based metalloradical catalysis. Metalloradical catalyst [Co(P1)], the cobalt(II) complex of D2h-symmetric porphyrin 3,5-DitBu-IbuPhyrin, was shown to be highly effective for selective intramolecular allylic C–H amination of both N-bishomoallylic and N-allylic sulfamoyl azides. The Co(II)-catalyzed intramolecular 1,6-C–H amination of these azides provides a general and efficient method to access the synthetically useful allylic 1,3-diamines under neutral and non-oxidative conditions, without complication from the competitive olefin aziridination. The origin of this remarkable chemoselectivity has direct relevance to the radical mechanism of Co(II)-based metalloradical amination.