Synthesis of diastereoisomeric BODIPY: An attempt on the resolution of axially chiral BODIPYs

This article provides efforts on a resolution of axially chiral BODIPYs (Ax*-BODIPY) towards Boron’s chiral utilization. Simply by generating the second chiral center on the dipyrromethene ring over the B-F substitution reaction, the Ax*-BODIPY will then turn to plausibly separable diastereoisomers, a column chromatographically separable molecule. By taking meso substituted p-bromophenyl-2,6-diethyl-1,3,5,7-tetramethylBODIPY as a successful model of conducting fluorine substitution reaction with methanol and ethanol, submission of racemic axially chiral meso substituted o-methoxyphenyl-2-bromo-6-ethyl-1,3,5,7-tetramethylBODPY to (S)-BINOL under the same conditions was unfortunately not succeded. The alternative route which is over B-Cl BODIPYs has successfully been synthesised from 2,4-dimethylpyrrole and 2-methoxybenzoylchloride followed by bromination, Vilsmeir-Haack condensation with 3-ethyl-2,4-dimethylpyrrole, and BCl3 chelation. However, the substitution of S-BINOL to the meso substituted o-methoxy-2-bromo-6-ethyl BCl2 BODYPY (11) was remaining unsuccessful.