Cycloaromatization reactions allow for construction of substituted arenes via thermal reactions of enediyne substrates. Mechanistically, these transformations are fascinating; however the high temperatures required and low product yields limit their utility as a synthetic tool. Previous studies in our lab demonstrated room temperature cyclizations of enediynes to arene products by the use of CpRu(MeCN)3+ or Cp*Ru(MeCN)3+. The current focus of this work is primarily on fundamental studies to establish the scope and limitations of thermal and ruthenium-mediated cycloaromatizations via an examination of nitrogen containing enediynes substrates. 2-(pent-1-yn-1-yl)-3-(prop-1-yn-1-yl)pyridine (1) was synthesized, and upon heating in the presence of bromoform and 1,4-CHD, led to the formation of two products: a mono-brominated quinoline derivative (2) and a quinoline derivative (3) . It is hypothesized that HBr is generated in-situ, which can then add across an alkyne to form a dienyne intermediate. This dienyne can undergo a Höpf-type cycloaromatization, formulating the mono-bromonated quinoline derivative. The quinoline product was hypothesized to form via protonation of the pyridine via HBr. The pyridinium enediyne is more electron-deficient, thus this substrate undergoes the Bergman cycloaromatization at a faster rate than the unprotonated enediyne.

Thermal and metal-mediated cycloaromatization reactions of conjugated tri-π systems

251st National Meeting (2016)

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