NEW METHOD FOR ISOMERIZATION OF (Z)-STILBENES INTO THE (E)-ISOMERS CATALYZED BY DIARYL DISULFIDE

A new method for isomerization of (Z)-stilbenes into the (E)-isomers, catalyzed by diaryl disulfide, has been developed. Diphenyl disulfide is the most versatile catalyst, smoothly effecting the isomerization of stilbene, methoxystilbenes, and hydroxystilbenes. For dimethoxystilbenes, whose isomerization by diphenyl disulfide is slow, 4,4'-dinitrodiphenyl disulfide or 2,2'-dipyridyl disulfide greatly accelearted the isomerization. Diphenyl disulfide is ineffective for the isomerization of stilbenes bearing electron-attracting substituent(s). The isomerization of these stilbenes was greatly accelerated by catalysts bearing an electron-donating substituent, such as 4,4'-dimethoxydiphenyl disulfide.