Diastereofacial selectivity of O-protected alpha-hydroxy aldehydes: Temperature and solvent effect

Temperature dependence measurements allow the evaluation of stereoselectivi ty in terms of differential enthalpy and entropy of activation,an analysis of diastereoselectivity in the addition reaction of nBuLi to O-protected al pha -hydroxy aldehydes revealed the great importance of the entropic contri bution in directing the facial diastereoselectivity. In many cases, the res ulting Eyring plots show an inversion temperature (T-inv). The existence of the T-inv as well as the enthalpic and entropic dominance of one diastereo isomer greatly depend on the reaction solvent.