Copper(I) mediated highly diastereoselective conjugate addition of Grignard reagents to functionalised cycloalkenols: a general and efficient route for the stereoselective synthesis of 5- and 6-membered ring trisubstituted cycloalkanols

The conjugate addition of magnesium cuprates to various 2-silyloxycyclopentene and 2-silyloxycyclohexene carboxylates leads diastereoselectively to related syn–anti cyclopentanols and cyclohexanols in fair overall yields. The β-elimination occurring with free hydroxylic derivatives is also partially or totally avoided by concomitant in situ trapping of the generated enolates. Attempts to rationalise our results are discussed.