REGIOSELECTIVE INTRODUCTION OF SUBSTITUENTS TO THE MESO-POSITION OF PYRROMETHENONE DERIVATIVE - APPLICATION TO THE SYNTHESIS OF STERICALLY FIXED PHYTOCHROME CHROMOPHORE ANCHORED TO THE C15 MESO-POSITION

Pyrromethenone derivatives corresponding to the CD-ring component of phycocyanobilin chromophore were regioselectively brominated with NBS at the meso-position retaining the stereochemistry of the olefinic carbon skeleton. Subsequent introduction of carbon-substituents to the brominated pyrromethenones was accomplished by treating with Grignard reagents to afford meso-alkylated (E)-isomers regardless of the stereochemistry of the starting brominated pyrromethenones. The resulting product was applied to the synthesis of a meso-anchored sterically fixed tetrapyrrole chromophore.