Ligand-Controlled Product Selectivity in Gold-Catalyzed Double Cycloisomerization of 1,11-Dien-3,9-Diyne Benzoates

A synthetic
method to prepare tricyclic bridged heptenones and
hexenones from gold­(I)-catalyzed double cycloisomerization of 1,11-dien-3,9-diyne
benzoates is described. A divergence in product selectivity was achieved
by fine-tuning the steric nature of the ligand of the Au­(I) catalyst.
In the presence of [MeCNAu­(JohnPhos)]+SbF6– (JohnPhos = (1,1′-biphenyl-2-yl)-di-tert-butylphosphine) as the catalyst, tandem 1,3-acyloxy
migration/metallo-Nazarov cyclization/1,6-enyne addition/Cope rearrangement
of the substrate was found to selectively occur to afford the bridged
heptenone adduct. In contrast, changing the Au­(I) catalyst to [MeCNAu­(Me4tBuXPhos)]+SbF6– (Me4tBuXPhos = di-tert-butyl­(2′,4′,6′-triisopropyl-3,4,5,6-tetramethyl-[1,1′-biphenyl]-2-yl)­phosphine)
was observed to result in the 1,11-dien-3,9-diyne benzoate undergoing
a more rapid tandem 1,3-acyloxy migration/metallo-Nazarov cyclization/[4
+ 2]-cyclization pathway to give the bridged hexenone derivative.