Coinage Metals-Catalyzed Cascade Reactions of Aryl Alkynylaziridines: Silver(I)-Single vs Gold(I)-Double Cyclizations

Alkynylaziridines carrying an aryl group could be efficiently
converted
into aminoallenylidene isochromans, isoquinolines, or tetrahydronaphtalenes
with silver­(I) salts and into 1-azaspiro[4.5]­decane derivatives with
gold­(I) complexes. Mechanistic investigations revealed that both Ag-
and Au-catalyzed reactions involved a Friedel–Crafts type intramolecular
reaction leading to an allene and that Au also rapidly promoted a
second intramolecular cyclization of the aminoallene intermediate
to the corresponding spiro derivative. Stereochemical investigations
suggested an anti-SN2′-type pathway
for the first cyclization leading to a stereodefined allene, which
could then be cyclized to the corresponding stereodefined spiro product.
These results highlight the duality between oxo- or azaphilicity and
alkynophilicity of Ag and Au as well as their complementarity in terms
of reactivity.