Reactivity of 2-benzylpyridyl lithium toward benzonitrile derivatives: Addition versus elimination

摘要

AbstractThis work investigated the reactivity of 2-benzylpyridyl lithium (2-Pyr)C(Ph)(R)Li (R?=?SiMe3,Li1; R?=?H,Li2) toward benzonitrile derivatives. Based on the different products, the reaction between lithium salts and nitriles might involve in addition, elimination and bimolecular coupling pathways, respectively. Treatment ofLi1with ArCN (Ar?= Ph,p-Tolyl,o-Tolyl,p-OMePh) yielded an addition intermediate pyridyl-1-aza-allyl-lithium [{(2-Pyr)C(Ph)C(Ar)N(SiMe3)}Li]2(1,Ar?= Ph) and its corresponding hydrolysis product 2-benzylpyridyl-ketone2–5, respectively, in which the reaction involved in a 1,3-shift of -SiMe3group to form a dimeric pyridyl-1-aza-allyl-lithium then followed by acidic hydrolysis. The MeOLi elimination reaction betweenLi2andp-MeO(C6H4)CN resulted in formation of 4-(2-benzylpyridyl)benzonitrile6. The reaction ofLi2withp-Me(C6H4)CN in the presence of TMEDA generated a 1:2 hydrolysis adduct 2-benzylpyridyl-enaminone7, however, in the absence of TMEDA it afforded a coupling product of bimolecular nitriles, 1-(4-methylphenyl)-2-cyanophenyl-ethanone8. We speculated the reaction mechanisms in sequence. The crys