Gas‐Phase Synthesis of 1‐Silacyclopenta‐2,4‐diene

Silole (1‐silacyclopenta‐2,4‐diene) was synthesized for the first time by the bimolecular reaction of the simplest silicon‐bearing radical, silylidyne (SiH), with 1,3‐butadiene (C₄H₆) in the gas phase under single‐collision conditions. The absence of consecutive collisions of the primary reaction product prevents successive reactions of the silole by Diels–Alder dimerization, thus enabling the clean gas‐phase synthesis of this hitherto elusive cyclic species from acyclic precursors in a single‐collision event. Our method opens up a versatile and unconventional path to access a previously rather obscure class of organosilicon molecules (substituted siloles), which have been difficult to access through classical synthetic methods.