Diastereofacial Selectivity of O‐Protected α‐Hydroxy Aldehydes: Temperature and Solvent Effect

Temperature dependence measurements allow the evaluation of stereoselectivity in terms of differential enthalpy and entropy of activation. An analysis of diastereoselectivity in the addition reaction of nBuLi to O-protected α-hydroxy aldehydes revealed the great importance of the entropic contribution in directing the facial diastereoselectivity. In many cases, the resulting Eyring plots show an inversion temperature (Tinv). The existence of the Tinv as well as the enthalpic and entropic dominance of one diastereoisomer greatly depend on the reaction solvent.