Hydroalumination of Ketenimines and Subsequent Reactions with Heterocumulenes: Synthesis of Unsaturated Amide Derivatives and 1,3-Diimines

The
series of differently substituted ketenimines 1 was hydroluminated
using di-iso-butyl aluminum
hydride. For the sterically congested ketenimine 1a,
preferred hydroalumination of the CN-bond was proven by X-ray
crystallography (compound 5a). In situ treatment of the
hydroaluminated ketenimines 5 with various heterocumulenes
like carbodiimides, isocycanates, isothiocyanates and ketenimines
as electrophiles and subsequent hydrolytic workup resulted in novel
enamine derived amide species in case of N-attack
(sterically less hindered ketenimines) under formation of a new C–N-bond
or in 1,3-diimines by C–C-bond-formation in case of bulky substituents
at the ketenimine-nitrogen atom. Furthermore, domino reactions with
more than 1 equiv of the electrophile or by subsequent addition of
two different electrophiles are possible and lead to polyfunctional
amide derivatives of the biuret type which are otherwise not easily
accessible.