Extra-Annulated Chlorophyll Derivatives by Scholl Reaction.

The ferric chloride assisted Scholl reaction of methyl (3,5-dimethoxyphenyl)carbonyl-pyropheophorbide- a produced an extra-annulated, didehydrogenated chlorophyll derivative with a six-membered ring fused at the pyrrole A-ring. The steric interaction of the substituents on the additional tetralone and B-rings induced molecular helicity. The helically cyclized stereoisomers were separated by recrystallization, and their ( P / M )-stereochemistry was confirmed by circular dichroism spectra. The distortion of their chlorin π-systems broadened electronic absorption bands to cover all visible regions and reach the near-infrared region.