Abstract
We report an efficient and practical iron-catalyzed hydrogen atom transfer protocol for assembling acetylenic motifs into functional alkenes. Diversities of internal alkynes could be obtained from readily available alkenes and acetylenic sulfones with excellent Markovnikov selectivity. An iron hydride hydrogen atom transfer catalytic cycle was described to clarify the mechanism of this reaction.
Highlights
Alkyne and its derivatives are important structural cores in diversities of bioactive compounds from natural products to pharmaceuticals and functional materials [1–3], which serve as versatile synthetic building blocks in organic synthesis [4–9]
Straightforward nucleophilic or electrophilic alkynylation of nucleophilic acetylides generated utilizing strong bases relying on their intrinsic acidity or electrophilic acetylide variants prepared through complex routes were considered as traditional strategies to assemble the alkyne moieties onto the organic skeletons for the construction of C–C bonds
Radical-mediated SOMOphilic alkynylation has made remarkable progress depending on the flourish development of radical chemistry, which provides reliable approaches for the formation of C–C bond
Summary
Alkyne and its derivatives are important structural cores in diversities of bioactive compounds from natural products to pharmaceuticals and functional materials [1–3], which serve as versatile synthetic building blocks in organic synthesis [4–9]. Acetylenic sulfones are usually treated as efficient radical acceptors, attached by the generated carbon radicals with excellent anti-Michael selectivity to afford enyl radical intermediates, achieving alkynyl functionalization with the realization of a sulfonyl radical via a sequential radical-mediated β-scission process (Scheme 1a) These reactions were amply explored by the efforts of organic chemical scientists (Scheme 1b). In 2006, Renaud and coworkers disclosed a radical-mediated alkynylation of alkenes to yield internal alkynes under the initiation of di-tert-butylhyponitrite, wherein the in situ hydroboration of the alkenes contributed to the excellent anti-Markovnikov selectivity (Scheme 1c) [68]. Acetylenic sulfones with methyl, methoxyl, phenyl, fluoro, chloro, bromo and trifluoromethyl groups engage in the Encouraged by the results of variable alkenes, we continued to investigate the scope of alkyne sources utilizing alkene 1m as a radical precursor under the optimal conditions.
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