Practical and Highly Stereoselective Synthesis of Trisubstituted (E)-α,β-Unsaturated Esters

Trisubstituted ( E )-α,β-unsaturated esters bearing various substituents were synthesized with high geometrical selectivity by using three reactions: an aldol reaction, acetylation of the hydroxy group at the β-position, and an E1cB reaction induced by 1,8-diazabicyclo[5.4.0]undec-7-ene. The method does not require separation of the diastereoisomeric mixture of β-hydroxy ester intermediates before the E1cB reaction, and is usable for gram-scale syntheses of trisubstituted ( E )-α,β-unsaturated esters.