ACID-CATALYZED AND BASE-CATALYZED ISOMERIZATION OF CIS-1,2-DIARYLACRYLONITRILES

The isomerization kinetics of as-l, 2-p-substituted-diphenylacrylonitriles and cís-l-aryl-2-phenylacrylonitriles (Ar = 2-furyl, 2-thienyl, 2-selenophenyl) have been studied in a solution of decahydronaphthalene with methanesulfonic acid and potassium tert-butoxide as catalysts. The acidic isomerization is slower than the basic one and is characterized by highly positive entropy changes. The substituents produce similar effects in both reactions. The general scheme of the isomerization includes (i) nucleophilic addition of the catalyst to the double bond, (ii) free rotation around the formed single bond, and (iii) elimination of the catalyst from the trans rotamer. In the acid isomerization, the heterocycle-containing acrylonitriles react faster than the phenyl derivative owing to the greater inductive effects and the lesser steric congestion of heterocycles. A satisfactory correlation of the reactivities with a combination of polar and steric effects is observed by an appropriate two-parameter equation. In the base-catalyzed isomerization a correlation with mesomeric constants of heterocycles is found. © 1979, American Chemical Society. All rights reserved.