Since their discovery by Burton and von Pechmann in 1887,[1] allenes have metamorphosed from a laboratory curiosity to a versatile and uniquely reactive functional group.[2] The C= C bond of allenes is around 10 kcal molÀ1 less stable than that of simple alkenes,[3] rendering them significantly more reactive. In transition-metal-catalyzed reactions their reactivity is closer to that of alkynes than that of simple alkenes. ...