Mn(I) C−H functionalization of coumarins provides a versatile and practical method for the rapid assembly of fused polycyclic pyridinium-containing coumarins in a regioselective manner. The synthetic strategy enables application of bench-stable organomanganese reagents in both photochemical- and thermal-promoted reactions. The cyclomanganated intermediates, and global reaction system, provide an ideal testing ground for structural characterization of the active Mn(I) carbonyl-containing species, including transient species observable by ultra-fast time-resolved spectroscopic methods. The thermodynamic reductive elimination product, solely encountered from reaction between alkynes and air-stable organometallic cyclomanganated coumarins, has enabled characterization of a critical seven-membered Mn(I) intermediate, detected by time-resolved infrared spectroscopy, enabling the elucidation of the temporal profile of key steps in the reductive elimination pathway. Quantitative data are provided. Manganated polycyclic products are readily decomplexed by AgBF4, opening-up an efficient route to the formation of π-extended hybrid coumarin-pyridinium compounds.
Bibliographical noteFunding Information:
The STFC (access to the ULTRA facility at the Rutherford Appleton Laboratories, Harwell UK) is gratefully acknowledged for funding, equipment, and support. We thank Syngenta (CASE award) for co‐funding an EPSRC CASE PhD studentship for T.J.B (doctoral training grant reference EP/ N509413/1), the University of York for a PhD studentship to J.B.E, the Royal Society of Chemistry for a research enablement grant (E21‐8424864227) and EPSRC for a responsive mode grant (EP/W031914/1). The Schlumberger Foundation is gratefully acknowledged for funding to support the PhD studies of M.K. We thank David Husbands for assistance with C NMR experiments. J.M.L. and I.J.S.F. acknowledge the Royal Society for Industry Fellowships (INF\R1\221057 and INF\R2\202122 respectively). The computational work in this project was undertaken on the Viking Cluster, which is a high‐performance computer facility provided by the University of York. We are grateful for computational support from the University of York High Performance Computing service, Viking and the Research Computing team. 13
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- infrared spectroscopy