Chiral Homoenolate Equivalents, V. Hydroxylakylation of Lithiated 3‐[(S)‐2‐(Methoxymethyl)pyrrolidino]‐1,3‐diphenylpropene – An Asymmetric Homoaldol Reaction

The hydroxyalkylation of lithiated 3‐[(S)‐2‐(methoxymethyl)‐pyrrolidino]‐1,3‐diphenylpropene (2) with aldehydes is completely regioselective giving homoaldol adducts in good yields. The simple diastereoselectivity is low with typical ratios ranging between 1:1 and 1:3 with the syn isomer predominating. The induced diastereoselectivity is much higher and is strongly solvent‐dependent. The reaction predominantly proceeds according to a metalloretentive mechanism from the si side of the allylic system in THF as well as in TBME. The induced diastereoselectivity obtained by the use of the less solvating TBME is considerably higher than in the strongly solvating THF, selectivities of up to 97% ee being reached.