Diazepane Carboxylates as Organocatalysts in the Diels–Alder Reaction of α-Substituted Enals
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.
H?ggman, Nicklas O.,Zank, Benjamin,Jun, HyunJune,Kaldre, Dainis,Gleason, James L.
supporting information
p. 5412 - 5416
(2018/10/20)
Chiral (Acyloxy)borane (CAB): A Powerful and Practical Catalyst for Asymmetric Diels-Alder Reactions
Chiral (acyloxy)borane complexes catalyze the Diels-Alder reaction of α,β-unsaturated aldehydes to bring about remarkable induction.