Catalyst-controlled torquoselectivity switch in the 4π ring-opening reaction of 2-amino-2-azetines giving β-substituted α,β-unsaturated amidines.

The torquoselectivity of the 4π electrocyclic ring-opening reaction of 2-azetines can be controlled by the Brønsted acidity of the catalyst and the polarity of the solvent. DFT calculations provided insight into the mechanism of this remarkable switch. Anti and syn stereoisomers of α,β-unsaturated amidines were selectively synthesized from ynamides and aldimines in the presence of Tf(2)NH and CSA, respectively.