Ruthenium(II)-Catalyzed C–H (Hetero)Arylation of Alkenylic 1,n‑Diazines (n = 2, 3, and 4): Scope, Mechanism, and Application in Tandem Hydrogenations

A general ruthenium­(II)-catalyzed methodology enabling the (hetero)­arylation of alkenylic C–H bonds utilizing a series of synthetically appealing diazines as directing groups is presented. Despite the presence of additional nitrogen lone pairs remote from the C–H bond activation site, which could eventually poison the catalyst, the reaction times are short (3 h), thus being suitable for selective double C–H bond arylation. Mixtures of E:Z isomeric products were observed in some cases, which were further hydrogenated in a tandem manner in the presence of the remaining ruthenium catalyst from the first step, representing an alternative approach to more difficult C­(sp3)–H bond functionalization. According to mechanistic studies, the unexpected E:Z product formation seems to occur by thermal CC bond isomerization after the reductive elimination step.