Triflimide-catalysed sigmatropic rearrangement of N-allylhydrazones as an example of a traceless bond construction.

The recognition of structural elements (that is, retrons) that signal the application of specific chemical transformations is a key cognitive event in the design of synthetic routes to complex molecules. Reactions that produce compounds without an easily identifiable retron, by way of either substantial structural rearrangement or loss of the atoms required for the reaction to proceed, are significantly more difficult to apply during retrosynthetic planning, yet allow for non-traditional pathways that may facilitate efficient acquisition of the target molecule. We have developed a triflimide (Tf(2)NH)-catalysed rearrangement of N-allylhydrazones that allows for the generation of a sigma bond between two unfunctionalized sp(3) carbons in such a way that no clear retron for the reaction remains. This new 'traceless' bond construction displays a broad substrate profile and should open avenues for synthesizing complex molecules using non-traditional disconnections.