Esters reactions with organoaluminum reagents

Treatment of pentafluorobenzaldehyde and 2-(phenylthio)propene with chiral organoaluminum reagent at -78 C for 1 h gave the ene adduct in 90% yield. The enantiomeric excess was determined by HPLC analysis to be 88% ee after converting to its MTPA ester. Here use of stoichiometric amounts of the chiral Lewis acid is indispensable. Attempted reaction of pentafluorobenzaldehyde and 2-(phenylthio)propene under the influence of catalytic amounts of (R)-l (10-20 mol%) gave no reproducible result in chemical as well as optical yields. However, the presence of 4A molecular sieves (activated powder) is capable of making the reaction ca ytic. Thus, the ene reaction of... 

With this procedure, organoaluminum reagents bearing ester moiety 15 can be prepared from allylic chloride 14 without suffering from the intramolecular addition to ester functionahty (Scheme 12). The reaction of 15 and 4 -bromoacetophenone provides bicyclic lactone as a single diastereomer. 

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