Introduction of a Third Meso Substituent into 5,10-Diaryl Chlorins and Oxochlorins

Abstract

Chlorins/oxochlorins bearing distinct patterns of substituents are valuable compounds in bioorganic and materials chemistry. Treatment of a 5,10-diaryl-substituted chlorin or oxochlorin with TFA-d(1) resulted in selective deuteriation of the remaining meso positions (15, 20) rather than any of the beta-pyrrolic positions. Electrophilic iodination or bromination of a 5,10-diaryl-substituted chlorin proceeded with high regioselectivity, affording the 5,10-diaryl-15-halo-substituted chlorin. Iodination or bromination of a free base 5,10-diaryloxochlorin gave a mixture of products arising through halogenation at the 15-, 20-, and beta-pyrrolic positions, while bromination of a zinc 5,10-diaryloxochlorin selectively gave the 5,10-diaryl-20-bromo-substituted oxochlorin. The Suzuki coupling reaction of a phenyl boronic acid derivative and a 5,10-diaryl-15-iodooxochlorin or 5,10-diaryl-20-bromooxochlorin gave the corresponding 5,10,15- or 5,10,20-triaryloxochlorin. The introduction of a third aryl substituent into the chlorin or oxochlorin causes an approximately 5-nm red shift of the long wavelength Q(y) absorption band. Two phenylethyne-linked oxochlorin-oxochlorin dyads in distinct metalation states (zinc/free base, free base/zinc) were prepared by Sonogashira coupling reactions of a 5,10-diaryl-20-bromooxochlorin and a 10-substituted ethynylphenyl oxochlorin. This study provides access to new chlorins/oxochlorins that can be utilized in diverse applications.