Ruthenium(II)-Catalyzed C–H (Hetero)Arylation of Alkenylic 1, n -Diazines ( n = 2, 3, and 4): Scope, Mechanism, and Application in Tandem Hydrogenations
Résumé
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 hours), 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(sp 3)-H bond functionalization. According to mechanistic studies, the unexpected E:Z product formation seems to occur by thermal C=C bond isomerization after the reduc-tive elimination step.
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