Cadmium iodide-mediated allenylation of terminal alkynes with ketones

Allenes are important building blocks in organic synthesis and have attracted much attention from researchers worldwide. So far, mono- and 1,3-disubstituted allenes can be prepared easily by applying the allenylation of terminal alkynes reaction of aldehydes. However, trisubstituted allenes have never been reported using this reaction due to the extremely low reactivity of ketones. Here, we report the one-pot synthesis of trisubstituted allenes from terminal alkynes and ketones utilizing cadmium iodide as the mediator. With this protocol, a series of different allenes, including 1,5-bisallenes and optically active allenols, which are especially important in synthetic chemistry, have been successfully prepared. The allenylation of terminal alkynes is a convenient route to allenes from simple starting materials, though previously limited to formaldehyde and aldehyde substrates. Here a method enabling the use of ketones is reported, giving easy access to trisubstituted allenes.