Rh(I)-Catalyzed Chemo- and Stereoselective Domino Cycloaddition of Optically Active Propargyl 2,4-Hexadienyl Ethers

1,1′-Bi-2-naphthol
in combination with ZnEt2,
Ti­(OiPr)4, and dicyclohexylamine have been employed
to catalyze asymmetric alkyne addition to an ynal to synthesize optically
active propargylic alcohols containing two alkyne functions with excellent
yields and enantioselectivities. These chiral alcohols are readily
converted to the corresponding optically active propargyl 2,4-hexadienyl
ethers. These diene-diyne substrates are found to undergo a highly
chemoselective and stereoselective domino Pauson–Khand and
Diels–Alder cycloaddition catalyzed by [RhCl­(CO)2]2 under CO to generate a class of tetracyclic compounds
with high enantiomeric purity. This is a very efficient method for
the asymmetric synthesis of polycyclic compounds.