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 sp2 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.
