STUDIES ON S-CIS S-TRANS PREFERENCE OF ACYCLIC ALPHA,BETA-UNSATURATED ESTERS - REACTIONS, SUPERSONIC JET SPECTROSCOPY, NOES, AND X-RAY-ANALYSIS

The s-cis/s-trans preference of acyclic alpha,beta-unsaturated esters has been studied by their reactions to elucidate the preference in the transition state and by supersonic jet spectroscopy, NOE experiments, and X-ray analysis to clarify the preference in the ground state. It has been widely accepted that enoate-Lewis acid complexes prefer the s-trans conformation not only in the ground state but also in the transition state of the reactions involving those complexes. The conjugate addition of metal amides to uncomplexed enoates proceeds predominantly through the s-cis conformation, and most organocopper conjugate additions in the absence of Lewis acids or related metal salts take place preferentially in the s-cis conformation. It is clarified that the relative population of the s-cis and s-trans conformer of uncomplexed methyl cinnamate is nearly 1:1 in a supersonic free jet and in solution at room temperature. X-ray analyses of 23 and 24 indicate the s-cis conformation, suggesting that most enoates adopt the s-cis form in the solid state except for 16-18.