A highly
efficient gold-catalyzed cycloisomerization of 1,5-diynes
was developed. Various functional groups are tolerated under the mild
reaction conditions, which provides an alternative approach for the
synthesis of indeno[1,2-c]furans. On the basis of
mechanistic studies, including crossover experiments, deuterium labeling,
and computational chemistry, the product formation proceeds via a
formal [5,5]-sigmatropic rearrangement, a yet unknown reactivity pattern
in gold catalysis. Instead of a synchronous concerted [5,5]-sigmatropic
rearrangement and beyond an asynchronous concerted mode, each involving
a single transition state, two energetically low transition states
(1.8 and 5.6 kJ/mol) and an intermediate associate of the migrating
benzyl cation and the vinyl gold species could be located in the computations.