Abstract
We have discovered a ring-opening fluorination of bicyclic azaarenes. Upon treatment of bicyclic azaarenes such as pyrazolo[1,5-a]pyridines with electrophilic fluorinating agents, fluorination of the aromatic ring is followed by a ring-opening reaction. Although this overall transformation can be classified as an electrophilic fluorination of an aromatic ring, it is a novel type of fluorination that results in construction of tertiary carbon–fluorine bonds. The present protocol can be applied to a range of bicyclic azaarenes, tolerating azines and a variety of functional groups. Additionally, mechanistic studies and enantioselective fluorination have been examined.
Highlights
Fluorine is one of the most important elements that could be installed onto hydrocarbon frameworks in pharmaceuticals, agrochemicals, and materials science.[1]
We selected 3-phenylpyrazolo[1,5-a]pyridine (1A) as the model substrate to examine electrophilic uorinating agents and reaction conditions (Table 1)
When using trimethylphenyl (1E) and naphthyl (1F) starting materials, the corresponding products 2E and 2F were obtained in moderate yields, and occurred decomposition of 1E or uorinated the aryl group of 1F
Summary
Fluorine is one of the most important elements that could be installed onto hydrocarbon frameworks in pharmaceuticals, agrochemicals, and materials science.[1]. We hypothesized that treating bicyclic azaarenes with an electrophilic uorinating agent would result in uorination at the C3 position, followed by deprotonation at the C2 position and pyrazole ring opening via N–N bond cleavage. We selected 3-phenylpyrazolo[1,5-a]pyridine (1A) as the model substrate (which was readily prepared in three steps from a commercially available compound) to examine electrophilic uorinating agents and reaction conditions (Table 1).
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