Enantioselective γ-Deprotonation of Alkyl-Substituted O-1,3-Butadien-2-yl Carbamates and Regioselective Asymmetric Homoaldol Reaction

This work presents a facile method for the construction of geometrically defined 1,3‐dien‐2‐yl carbamates. Their highly stereoselective asymmetric deprotonation with the chiral base pair n‐butyllithium/(–)‐sparteine (2) and substitution reactions allows the flexible synthesis of substituted stereohomogeneous 1,3‐dienes. Diastereo‐ and enantioselective homoaldol reactions with aldehydes are possible after transmetallation of the lithium species with ClTi(NEt2)3. Intensive investigations for the interpretation of the stereochemical outcome of the reactions of each carbamate are also presented. Comparison of all results shows common properties of the allyllithium intermediates as well as surprising differences, which indicate a strong relationship between the structure of these intermediates and their reactivity. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2007)