OPTICALLY-ACTIVE (E,Z)-1,3-CYCLOOCTADIENE - FIRST ENANTIOSELECTIVE SYNTHESIS THROUGH ASYMMETRIC PHOTOSENSITIZATION AND CHIROPTICAL PROPERTY

Enantiodifferentiating photoisomerizations of (Z,Z)-1,3-cyclooctadiene (1ZZ) to the chiral E,Z-isomer 1EZ were performed at varying temperat ures in the presence of some benzenepoly-, naphthalene(di)-, and anthr acene-carboxylates. Of these chiral sensitizers, (-)-menthyl benzenehe xacarboxylate afforded the highest enantiomeric excesses (ee's) up to 10% and 18% in pentane at 25 and -40 degrees C, respectively. In contr ast, the use of polar solvents greatly diminished the product's ee, su ggesting intervention of a radical ionic rather than exciplex intermed iate in these solvents. Optically pure 1EZ is shown to possess anomalo usly high specific rotation and circular dichroism as a simple diene c hromophore: [alpha](25)(D) 1380 degrees (CH2Cl2), Delta epsilon 12.8 M (-1) cm(-1) (lambda(ext) 228 mm, cyclohexane). The chiroptical propert ies observed not only correct the previous data but also present the c onclusive evidence for the recent theoretical predictions.