Regioselective Stepwise Bromination of Boron Dipyrromethene (BODIPY) Dyes

Halogenated BODIPYs are important synthetic precursors
and potential
sensitizers for photodynamic therapy (PDT). Electrophilic bromination
of pyrrolic-unsubstituted BODIPYs using bromine regioselectively generated
mono- to heptabromoBODIPYs in a stepwise fashion in good to excellent
yields. These resultant bromoBODIPYs were applied for regioselective
substitution and Suzuki coupling reaction to generate BODIPYs 4, 5, 6, and 7 in good
to excellent yields. According to NMR and X-ray analysis results,
the stepwise bromination first takes place at 2,6-, then at 3,5-,
and eventually at 1,7-positions, whereas the regioselective substitution
occurs first at 3,5- then at 1,7-positions of the chromophore. The
spectroscopic properties of these resultant BODIPYs were studied,
which shows the potential application of these bromoBODIPYs as sensitizers
for PDT.