Carboxalkylation of Enolates with Menthyl Chloroformate. Diastereoselective Formation of Quaternary Carbon Centers

Diastereomeric rations of 90 : 10 to > 95 : 5 are reached when carboxylic acid, ketone, and ester-derived enolates 2, 7a/7b, 10, and 13 are allowed to react with (-)-menthyl chloroformate 1 to deliver nonracemic compounds which contain stereogenic quaternary carbon centers.