Studies on the α-acetylation of δ-valerolactone and ε-caprolactone

The synthetic approach to α-acetylated δ-valero- () and ε-caprolactone () is reported. While was isolated in 21% yield from the respective iodoester by an alkylation sequence involving transesterification and Finkelstein reaction, was not obtained from but the dimer . Also transesterification and olefin ring closing metathesis (RCM) failed to prepare . RCM resulted in the dimeric lactone , showing that the formation of 14-membered rings is favored over that of seven-membered rings. A Mukaiyama-type Claisen reaction finally gave α-acetyl lactones in practically useful quantity of about 10 g (62% yield): starting lactones were converted to silylenolethers , which were acetylated with acetic anhydride in presence of the Lewis acid catalyst TiCl4. However, acetylation depends on the addition sequence of starting materials: if the mixture of Ac2O/TiCl4 is added to , lactone can be further converted to give bis-oxepanonyl ethanols . Both compounds were characterized by X-ray crystallography and NMR.