The lithium salt of trimethylsilyldiazomethane (TMSC (Li) N₂) smoothly reacts with alkyl aryl ketones and aldehydes to give the corresponding homologous alkynes via alkylidene carbene intermediates. In the case of aliphatic ketones, the resulting alkylidene carbenes can be trapped by an amine to afford enamines which are efficiently converted to the homologous aldehydes. TMSC (Li) N₂ can also be effectively used for the preparation of heterocycles such as 2, 3-dihydrofurans, cyclohepta [b] pyrrol-2-ones, and 3-pyrrolines from the corresponding β-siloxyketones, N-methylanilides of α-keto acids, N, N-dialkylamides of α-keto acids, and N, N-disubstituted α-amino ketones, respectively.