Reactivity of N-Boc-Protected Amino-Ynones in the Presence of Zinc Chloride: Formation of Acetylenic Cyclic Imines and Their Palladium Complexes
Abstract
Amino-ynones can be seen as precursors of various heterocyclic rings. Although γ-amino-ynones have been used to prep. exocyclic vinylogous amides in the presence of Bronsted acids, we describe here the use of zinc chloride as a weak Lewis acid for their conversion into acetylenic cyclic imines. This reaction, which was attempted for a diverse range of γ-amino-ynones, proved to be robust and efficient in most cases and was easily extended to δ-amino-ynones to yield various acetylenic cyclic imines. Depending on the workup procedure, the latter compds. could be isolated either as free org. compds. or as zinc complexes. The ability of these cyclic imines to form complexes with palladium is also reported.