The first examples of early-transition-metal-catalyzed hydroaminoalkylation reactions
of allenes are reported. Initial studies performed with secondary aminoallenes led
to the identification of a suitable titanium catalyst and revealed that under the
reaction conditions, the initially formed hydroaminoalkylation products undergo an
unexpected titanium-catalyzed rearrangement to form the thermodynamically more stable
allylamines. The assumption that this rearrangement involves a reactive allylic cation
intermediate provides a simple explanation of the fact that no successful early-transition-metal-catalyzed
hydroaminoalkylations of allenes have previously been reported. As a result of the
generation of the corresponding cation, the titanium-catalyzed intermolecular hydroaminoalkylation
of propa-1,2-diene unexpectedly gives an aminocyclopentane product formed by incorporation
of two equivalents of propa-1,2-diene.
Key words
allenes - amines - C–H activation - homogeneous catalysis - titanium - hydroaminoalkylation
