Titanium(IV) chloride catalyzed cyanation of benzylic halides with trimethylsilyl cyanide

Six sterically hindered benzylic chlorides have been substituted with cyano groups in excellent yields with trimethylsilyl cyanide and titanium tetrachloride in methylene chloride. Both monochloro substrates such as diphenylmethyl chloride and triphenylmethyl chloride and dichloro substrates such as dichlorodiphenylmethane and sym-tetraphenylethylene dichloride were studied. Because isonitriles are plausible reaction intermediates, the isomerization of trityl isonitrile by TiCl 4 and by trityl tetrafluoroborate was studied at 0 and -78 o C. Both reagents catalyze conversion to triphenylacetonitrile at 0 o C while only trityl tetrafluoroborate is effective at -78 o C