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.

Copper-Catalyzed Borylative Cyclization of Substituted N-(2-Vinylaryl)benzaldimines.

A t-BuOCu-initiated reaction sequence of styrene borometalation and intramolecular imine addition has been achieved using a Cu(OTf)2/dppf combination as catalyst. The product of this reaction cascade is a useful 2,3-disubstituted indoline bearing a versatile boryl moiety and is formed with sole cis-selectivity. To account for the observation of the exclusive formation of cis-stereoisomers, a transition state featuring copper-imine coordination is suggested. The application to the synthesis of antioxidant tetrahydroindenoindoles is described.

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

A range of novel (poly)cyclic alkaloids incorporating an unprecedented 1,5-diazaspiro[2.4]heptane core that carry a spiro NH aziridine moiety and a 7-vinyl group are constructed from the thermal reaction of vinyl azides with tethered alkenes. Vinyl azides are converted to 2H-azirines in situ, which serve as enophiles for intramolecular imino-ene reactions with suitable alkenes. High stereoselectivity and specificity have been achieved for this novel intramolecular imino-ene reaction of azirines.