Variable Stereocontrol in Cycloadditions of 1,7,9-Decatrien-3-ones by Different Lewis Acidic Promoters – Application to a Short Synthesis of α-Eudesmol

Trienones 1–3 were subjected to Lewis acid-promoted intramolecular Diels–Alder reactions. It was shown that with monocoordinating Lewis acids the endo selectivity of the cycloaddition was generally high. The preference for either of the two possible endo products cis-a and cis-b, however, was shown to be highly dependent on the nature of the Lewis acid, and on the substitution pattern of the trienone substrates. Lewis acids with two coordination...