The development of an efficient oxidative [2,3]-sigmatropic rearrangement of allylic hydrazides, via singlet N-nitrene intermediates, is reported. The requisite allylic hydrazide precursors are readily prepared and undergo smooth sigmatropic rearrangement upon exposure to iodosobenzene. The products of this novel transformation are shown to be useful precursors to a variety of compounds.

A one-pot synthesis of allenes by the 2-nitrobenzenesulfonylhydrazide-mediated coupling of hydroxyaldehydes or ketones with alkynyl trifluoroborate salts is reported. This mild process involves in situ formation of a sulfonylhydrazone that reacts with alkynyl trifluoroborates to generate a transient propargylic hydrazide species. Decomposition of this unstable hydrazide via an intermediate monoalkyldiazine produces the allene products through an alkene walk mechanism.

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.

A new copper(II) chloride-promoted rearrangement of N-allylhydrazones has been developed. Treatment of a number of aromatic N-allylhydrazones with copper(II) chloride provides the formation of both a new carbon−carbon bond and a carbon−chlorine bond in the same reaction. Substrate studies revealed that the carbon−carbon bond-forming step proceeds by way of a concerted [3,3] sigmatropic rearrangement and selectively generates trans-substituted alkenes.

A new method for the stereoselective synthesis of dienes from aldehydes and N-allylhydrazine derivatives has been developed. High levels of (E)-stereoselectivity are obtained for a variety of substrates. Addition of a dienophile to the reaction mixture allows a one-flask diene synthesis-cycloaddition sequence.