Zirconium-Catalyzed Hydroaminoalkylation of Alkynes for the Synthesis of Allylic Amines

A zirconium-catalyzed
hydroaminoalkylation of alkynes to access α,β,γ-substituted allylic amines in an atom-economic fashion is reported.
The reaction is compatible with N-(trimethylsilyl)­benzyl­amine
and a variety of N-benzyl­aniline substrates,
with the latter giving the allylic amine as the sole organic product.
Various internal alkynes with electron-withdrawing and electron-donating
substituents were tolerated. Model intermediates of the reaction were
synthesized and structurally characterized. Stoichiometric studies
on key intermediates revealed that the open coordination sphere at
zirconium, imparted by the tethered bis­(ureate) ligand, is crucial
for the coordination of neutral donors. These complexes may serve
as models for the inner-sphere protonolysis reactions required for
catalytic turnover.