Ag-Catalyzed Insertion of Alkynyl Carbenes into C-C Bonds of β-Ketocarbonyls: A Formal C(sp 2 ) Insertion.

Here we report a silver-catalyzed alkynyl carbene insertion into β-ketocarbonyls using alkynyl N -nosylhydrazones as alkynyl carbene precursors, which provides access to trisubstituted allenyl ketones. This reaction represents the first example of an alkynyl carbene insertion into a C-C σ bond, affording products homologated with an sp ² carbon center. The products are useful substrates for further transformations. Experimental investigations and theoretical calculations suggest the reaction proceeds through a stepwise enol cyclopropanation/retro-aldol pathway.