Determination of the activation parameters and the mechanism for atropisomerization of (S)-3-(2-chlorophenyl)-2-[2-(6-diethylaminomethylpyridin-2-yl)vinyl]-6-fluoroquinazolin-4(3H)-one

Values of DeltaH double dagger (;)=111.6 +/-0.3 kJ mol(-1) (26.7 +/-0.1 kca l mol(-1)) and DeltaS double dagger=-25.7 +/-0.9 J K-1 mol(-1) (-6.1 +/-0.2 cal K-1 mol(-1)) have been determined for the atropisomerization of (S)-3- (2- chlorophenyl)-2-[2-(6-diethylaminomethylpyridin-2-yl)vinyl]-6-fluoroqui nazolin-4(3H)-one in decane. Based on molecular mechanics calculations in t he literature and an observation that more polar solvent does not increase isomerization rate, it is proposed that the isomerization occurs via a plan ar non-ionic transition state in which the carbonyl oxygen and the 6-chloro substituent are coplanar with each other.