Medium ring stereocontrol in the functionalisation of eight-membered lactones

Medium ring lactones with up to three substituents have been prepared as si ngle diastereoisomers via Claisen rearrangement. Application of medium ring stereocontrol to a gamma,delta-unsaturated eight-membered ring lactone pre pared by this route enabled the overall diastereoselective functionalisatio n of all but one of the ring positions. A comparison of the ring-induced se lectivity was made with that of the corresponding acyclic hydroxy ester whi ch exhibited an overall reversal of stereoselectivity. This methodology pro vides access to highly substituted polyketide fragments. (C) 1999 Elsevier Science Ltd. All rights reserved.