A highly efficient asymmetric synthesis of a 4,4-disubstituted butan-4-olide by the 1,7-asymmetric inductive addition of Grignard reagents to γ-keto esters

An efficient asymmetric synthesis of a butan-4-olide having a quaternary asymmetric carbon centre was achieved with up to 97% enantiomeric excess (e.e.) by the 1,7-asymmetric inductive addition of Grignard reagents to the γ-keto esters 4–7, the e.e. of which was highly dependent on the structure of the chelating group of the chiral auxiliaries 1–3.