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.
New methods for the synthesis of 1,3-diaryltriazenes and azo dyes from aryl amines are reported. Both methods involve the formation of aryl diazonium intermediates via the transnitrosation of aryl amines with N–nitrososulfonamides. Each two-step transformation may be performed in one reaction vessel at room temperature with no precautions taken to exclude air or moisture. Several triazene and azo dye structures are reported here for the first time, demonstrating the utility of operating the two-step reaction sequence under mild conditions.
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