We report experimental and computational evidence for nitrogen−fluorine halogen bonding in Ag(I)initiated radical C−H fluorinations. Simple pyridines form [N−F−N] + halogen bonds with Selectfluor to facilitate singleelectron reduction by catalytic Ag(I). Pyridine electronics affect the extent of halogen bonding, leading to significant differences in selectivity between mono-and difluorinated products. Electronic structure calculations show that halogen bonding to various pyridines alters the single-electron reduction potential of Selectfluor, which is consistent with experimental electrochemical analysis. Multinuclear correlation NMR also provides spectroscopic evidence for pyridine halogen bonding to Selectfluor under ambient conditions.
We
report a new method for regioselective aromatic bromination
using lactic acid derivatives as halogen bond acceptors with N-bromosuccinimide (NBS). Several structural analogues of
lactic acid affect the efficiency of aromatic brominations, presumably
via Lewis acid/base halogen-bonding interactions. Rate comparisons
of aromatic brominations demonstrate the reactivity enhancement available
via catalytic additives capable of halogen bonding. Computational
results demonstrate that Lewis basic additives interact with NBS to
increase the electropositive character of bromine prior to electrophilic
transfer. An optimized procedure using catalytic mandelic acid under
aqueous conditions at room temperature was developed to promote aromatic
bromination on a variety of arene substrates with complete regioselectivity.
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