Novel Preparation of b-lactones

b-Lactones are normally prepared using the Wynberg procedure - addition of a ketone to an aldehyde in the presence of a chiral catalyst (e.g. quinine) and this process has been commercialised by Lonza for the manufauture of optically active malic and citromalic acids. An intramolecular variant of this methodology has now been demonstrated, but is shown to proceed via a nucleophile-catalysed aldol-lactonisation mechanism rather than the possible 2+2 cycloaddition (Cortez G S et al J Am Chem Soc 2001, 123, 7945). The ketone is generated "in-situ" using Mukaiyama's reagent.