Intramolecular Imino-ene Reaction of 2H-azirines with Alkenes: Rapid Construction of Spiro NH Aziridines from Vinyl Azides

An aryl thiol-vinyl azide coupling reaction and a thiol-vinyl azide coupling/cyclization cascade: efficient synthesis of β-ketosulfides and arene-fused 5-methylene-2-pyrrolidinone derivatives

The addition reaction of thiol to vinyl azide has been extensively studied. Variously substituted aryl thiols are all viable for this coupling process. The scope of the other partner is successfully expanded from α-aryl vinyl azide to α-alkyl vinyl azide. A thiol-vinyl azide coupling/cyclization cascade is realized with substituted aryl vinyl azides carrying a 2-methoxycarbonyl group. The value of β-ketosulfide products was demonstrated by its application in S-heterocycle synthesis.

Intramolecular Alder-ene cycloisomerization of cyclopropenes with alkenes to access spirocycles

An Alder-ene cycloisomerization creates 3D-shaped spirocycles from cyclopropenes.

Copper-catalyzed [2+3]-annulation of N-H imines with vinyl azides: access to polyaryl 2H-imidazoles

A practical method for the synthesis of 2H-imidazoles via a [2+3] annulation of N-H imines with vinyl azides using a copper catalyst is developed. In this conversion, environmentally friendly oxygen is used as the sole oxidant and N2 and H2O are the only by-products. The catalytic transformation, operating under mild conditions, is operationally simple and is considered as a readily available catalytic system having good substrate and functional compatibility with high atom-efficiency without the need for additional ligands or additives.

B(C6 F5 )3 /Chiral Phosphoric Acid Catalyzed Ketimine-Ene Reaction of 2-Aryl-3H-indol-3-ones and α-Methylstyrenes

The enantioselective ketimine-ene reaction is one of the most challenging stereocontrolled reaction types in organic synthesis. In this work, catalytic enantioselective ketimine-ene reactions of 2-aryl-3H-indol-3-ones with α-methylstyrenes were achieved by utilizing a B(C₆ F₅ )₃ /chiral phosphoric acid (CPA) catalyst. These ketimine-ene reactions proceed well with low catalyst loading (B(C₆ F₅ )₃ /CPA=2 mol %/2 mol %) under mild conditions, providing rapid and facile access to a series of functionalized 2-allyl-indolin-3-ones with very good reactivity (up to 99 % yield) and excellent enantioselectivity (up to 99 % ee). Theoretical calculations reveal that enhancement of the acidity of the chiral phosphoric acid by B(C₆ F₅ )₃ significantly reduces the activation free energy barrier. Furthermore, collective favorable hydrogen-bonding interactions, especially the enhanced N-H⋅⋅⋅O hydrogen-bonding interaction, differentiates the free energy of the transition states of CPA and B(C₆ F₅ )₃ /CPA, thereby inducing the improvement of stereoselectivity.

Ag-Catalyzed cycloisomerization of 1,6-enynamide: an intramolecular type II Alder-ene reaction

An unusual type II Alder-ene cycloisomerization of 1,6-enynamide to fused bicyclic N-heterocycles is achieved by silver catalysis. 6-Endo-trig cyclization of a keteneiminium silver intermediate is proposed as the key step.

I2/TBHP mediated diastereoselective synthesis of spiroaziridines

A simple metal free protocol for the diastereoselective synthesis of spiroaziridines using easily accessible substrates is disclosed.

Visible light triggered photo-decomposition of vinyl azides to (E)-stilbene derivatives via 1,2-acyl migration

An efficient photocatalyst-free visible light assisted synthetic route to various (E)-stilbene derivatives was developed. The reaction proceeds through a denitrogenative photo-decomposition of vinyl azides into 2H-azirines followed by neighboring amino group assisted ring opening, 1,2-acyl migration and enolization. The photochemical reaction offers light harvesting without any photocatalyst to access a wide variety of substituted (E)-stilbenes in moderate to high yields.

Intramolecular Imino-ene Reaction of Azirines: Regioselectivity, Diastereoselectivity, and Computational Insights

Intramolecular imino-ene reaction of 2 H-aziridine has been studied experimentally and computationally, demonstrating that (1) the concerted process takes place regioselectively on the alkene E-CH group; (2) the geometry of the N-linker impacts the reaction activation energy and diastereoselectivity significantly, with pyramidal alkyl amine as the linkage, an exclusive cis-product is achieved; (3) when the reaction has to occur with the Z-CH group, the cis-diastereoselectivity is solely observed regardless of the nature of the N-linkage.