Titanium-Catalyzed Cyano-Borrowing Reaction for the Direct Amination of Cyanohydrins with Ammonia

Formation of Radical-like NH Ligand from NH3 at Ambient Conditions Mediated by Dialkyl Rare-Earth Complexes

Although intensive work on ammonia activation has been carried out in recent decades, generating nitrogen-centered radicals from NH3 under ambient conditions remains quite challenging. In the presented research, the conversion of NH3 to radical-like NH ligand has been achieved by the reactions of a series of dialkyl rare-earth (RE) complexes (1-RE, RE = Tb, Dy, Y, Ho, Er, Yb, and Lu) supported by β-diketiminate ligands with NH3 in n-hexane at room temperature, resulting in the formations of the radical-like μ3-NH ligands containing trinuclear RE complexes (2-RE). The radical-like feature of the μ3-NH ligand was revealed by electron paramagnetic resonance and magnetic measurements, radical trapping experiments, and computational spin density analysis. In addition, H2 was detected to form during the reaction of 1-RE with NH3, indicating that the radical-like μ3-NH ligand was likely to be generated via N-H bond homolysis. Moreover, the solvents and coordination pattern of β-diketiminate ligands are crucial for the formation of the radical-like μ3-NH ligand from NH3. When toluene instead of n-hexane was used in the reaction of 1-RE with NH3, an array of octaamido tetranuclear RE complexes (3-RE) was obtained. The reaction of the dialkyl yttrium complex (4-Y) bearing a modified β-diketiminate ligand, in which the two mesityl substituents are replaced by a 2,6-diisopropylphenyl group and a 2-(dimethylamino)ethyl group, with NH3 in both n-hexane and toluene only yielded a tetranuclear yttrium complex carrying the dianionic closed-shell μ3-NH ligands (5-Y).

Copper-Catalyzed Aza-Benzyl Transfer Michael Addition via C-C Bond Cleavage

A non-noble Cu-catalyzed transfer aza-benzyl Michael addition via the C-C bond cleavage of aza-benzyl alcohols has been disclosed. The unstrained C(sp³)-C(sp³) bond of an alcohol was selectively cleaved. This aza-benzyl transfer strategy provides a selective and environmentally benign approach for the C-alkylation of α,β-unsaturated carbonyl compounds that employs readily available alcohols as carbon nucleophiles and is characterized by a wide range of substrates and good to excellent yields.

Sliver-Catalyzed 1,3-Aza-Benzyl Migration of Allyl Alcohol

Carbon migration of alkenyl alcohols has been recognized as an increasingly viable methodology in organic synthesis. Herein, we disclose a silver-catalyzed 1,3-aza-benzyl migration of allyl alcohols by utilizing chelation-assisted selective cleavage of an unstrained C(sp³)-C(sp³) bond. This approach provides an available, efficient, high atom-economic, and environmentally benign procedure, leading to alkylation products with broad substrate scopes and excellent yields. The migration proceeds via a one-pot, two-step process involving a free-state alkyl metal species.

Alkynyl Borrowing: Silver-Catalyzed Amination of Secondary Propargylic Alcohols via C(sp3)-C(sp) Bond Cleavage

The silver-catalyzed alkynyl borrowing amination of secondary propargyl alcohols via C(sp³)-C(sp) bond cleavage has been developed. This new strategy was based on the β-alkynyl elimination of propargyl alcohols and alkynyl as the borrowing subject. This alkynyl borrowing amination featured high atom economy, wide functional group tolerance, and high efficiency.

Copper-catalyzed transfer methylenation via C(sp3)–C(sp3) bond cleavage of alcohols

Transfer Methylenation: A copper-catalyzed transfer methylenation via the cleavage of unstrained C(sp3)-C(sp3) bonds is developted. This is a de novo report for transfer hydrocarbylation between alcohols and carbonyl compounds.

2-Pyridinylmethyl borrowing: base-promoted C-alkylation of (pyridin-2-yl)-methyl alcohols with ketones via cleavage of unstrained C(sp3)–C(sp3) bonds

2-Pyridinylmethyl Borrowing: Transition-metal-free 2-pyridinylmethyl borrowing C-alkylation of alcohols access to ketones is developed. This unstrained C(sp3)–C(sp3) bonds cleavage of unactivated alcohols avoids the use of transition metals.

Tris(pentafluorophenyl)borane-Catalyzed Formal Cyanoalkylation of Indoles with Cyanohydrins

Despite the significant achievements related to the C3 functionalization of indoles, cyanoalkylation reactions continue to remain rather limited. We herein report on the formal C3 cyanoalkylation of indoles with cyanohydrins in the presence of a tris(pentafluorophenyl)borane (B(C₆F₅)₃) catalyst. It is noteworthy that cyanohydrins are used as a cyanoalkylating reagent in the present reaction, even though they are usually used as only a HCN source. Mechanistic investigations revealed the unique reactivity of the B(C₆F₅)₃ catalyst in promoting the decomposition of a cyanohydrin by a Lewis acidic activation through the coordination of the cyano group to the boron center. In addition, a catalytic three-component reaction using indoles, aldehydes as a carbon unit, and acetone cyanohydrin that avoids the discrete preparation of each aldehyde-derived cyanohydrin is also reported. The developed methods provide straightforward, highly efficient, and atom-economic access to various types of synthetically useful indole-3-acetonitrile derivatives containing α-tertiary or quaternary carbon centers.

Transition-metal free cyano 1,3 migration of unsaturated cyanohydrins

A novel approach of transition-metal-free cyano 1,3-migration of β,γ- and α,β-unsaturated cyanohydrins is reported.

Cyano-borrowing: titanium-catalyzed direct amination of cyanohydrins with amines and enantioselective examples

The direct amination of cyanohydrins with amines via a catalytic cyano-borrowing reaction was developed. The transformation features broad substrate scope, excellent functional group compatibility, and very mild and simple operations. Moreover, a titanium catalyst supported by quinine and (S)-BINOL ligands enabled an asymmetric cyano-borrowing reaction with moderate to high enantioselectivity.