21 hl Through the use of E ~ ( fod ) ~ catalysis? the silyloxy diene 1912 reacts with the appropriate aromatic aldehyde to give enol ethers 20a6 and 20b6 in nearly quantitative yield. Compound 20b was hydrolyzed to the 2,6-disubstituted tetrahydropyrone 216 with aqueous HC1-THF. Thus, the endo selectivity of the europium-induced pericyclic reac- tion5 provides a stereospecific entry to cis-2,6-disubstituted tetrahydropyrones. Alternative possibilities for taking ...
