An Organocatalytic Cope Rearrangement

The first example of an organocatalytic Cope rearrangement is reported. Acyclic and cyclic acyl hydrazides catalyze the rearrangement of 1,5‐hexadiene‐2‐carboxaldehydes via iminium ion formation. A correlation between ring size and catalyst activity was observed for the cyclic hydrazides, with seven‐ and eight‐membered‐ring catalysts being the most active. Diazepane carboxylate 5 c (10 mol %) catalyzed the rearrangement of a range of dienes at room temperature in acetonitrile using triflic acid as a co‐catalyst. Preliminary proof of principle for asymmetric catalysis was provided by rearrangement of 3,3‐dimethyl‐7‐phenyl‐1,5‐heptadiene‐2‐carboxaldehyde in the presence of a novel 7‐substituted diazepane carboxylate. Seven‐membered catalysts: Diazepane carboxylates catalyze the Cope rearrangement of 1,5‐hexadiene‐2‐carboxaldehydes under mild conditions. This process constitutes the first example of an organocatalytic Cope rearrangement and highlights the efficient formation of α‐substituted iminium ions with diazepane carboxylates.