Intermolecular Homopropargyl Alcohol Addition to Alkyne and a Sequential 1,6-Enyne Cycloisomerization with Triazole-Gold Catalyst

While gold-catalyzed homopropargyl
alcohol cyclization is a known
process, a triazole-gold catalyst prevented the intramolecular cyclization
in the presence of terminal alkynes. As a result, an intermolecular
addition to an alkyne was achieved. A sequential 1,6-enyne cycloisomerization
gave the unusual 2,3-dihydrooxepine, which revealed another new reaction
path. Diels–Alder reaction of oxepine followed by a 1,3-alkoxyl
shift gave hydrobezofuran derivatives in high yields. Diasterioselective
reaction of homopropargyl alcohol to final product enabled one-step
formation of five stereogenic centers with excellent enantiomeric
selectivity.