CATALYTIC ENANTIODIFFERENTIATION - THE TRANS-]-CIS-ISOMERIZATION OF (+/-)-1-ACETYLCYCLOOCTENE INDUCED BY CHIRAL AMINES

Irradiation of cis-acetylcyclooctene (c-ACO) gives a photostationary mixture of cis and trans ACO. t-ACO is stable in carefully dried acetonitrile. The thermal trans --> cis isomerization is induced by various catalysts, including protic or basic species. Optically active catalysts cause partial kinetic resolution of racemic t-ACO. This reaction is investigated in detail with (+)-ephedrine as a catalyst and with some 10 other structurally related inductors. The absolute configuration of t-ACO is deduced from calculations. It is found that each enantiomer of t-ACO exists in a cisoid and transoid conformer of opposite sign of CD in equilibrium. We observe a relation between structure and catalytic effect: for asymmetric catalysis the structural element of an alkylamino group attached to an asymmetric carbon is necessary. This suggests that the cisoid conformer of higher energy enters into the asymmetrically catalyzed isomerization.