Ethyl diazepane carboxylate efficiently catalyzes the Diels–Alder cycloaddition of α‐substituted‐α,β‐unsaturated aldehydes via iminium ion organocatalysis. The reaction is applicable to a range of dienes and dienophiles and generally proceeds at room temperature in the presence of 5 mol‐% catalyst and 2.5 mol‐% triflic acid co‐catalyst. The incorporation of a stereogenic center on the diazepane backbone in combination with a menthyl carbamate produces a catalyst which affords enantioselectivities of 70–95 % ee for the cycloaddition of cyclopentadiene with a range of dienophiles. The enantioselectivity is rationalized via a transition state in which electrostatic stabilization by the carboxylate directs the diene to the more hindered face of the dienophile.
The conjugate addition of indoles to α‐substituted enals is achieved by using a diazepane carboxylate catalyst under mild conditions (20 mol‐% catalyst, 20 mol‐% TFA, acetonitrile, –20 °C). The low basicity and high nucleophilicity of this catalyst overcomes the limitations of allylic 1,3 strain in the intermediate iminium ions, which is normally observed with secondary‐amine catalysts. Conjugate addition of a series of substituted indoles as well as electron‐rich aromatics with a variety of α‐substituted enals is demonstrated.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.