A2B- and A3‑Type Boron(III)Subchlorins Derived from meso-Diethoxycarbonyltripyrrane: Synthesis and Photophysical Exploration

• Published in: Journal of organic chemistry 2021-08, Vol.86 (15), p.10280-10287
• Main Authors: Soman, Rahul, Chandra, Brijesh, Bhat, Ishfaq A, Kumar, B. Sathish, Hossain, Sk Saddam, Nandy, Sridatri, Jose, K. V. Jovan, Panda, Pradeepta K
• Format: Article
• Language: English
• ISSN: 0022-3263; 1520-6904
• DOI: 10.1021/acs.joc.1c01001

The first direct fabrication of A2B- and A3-type B­(III)­subchlorins from meso-ethoxycarbonyl-substituted tripyrrane has been realized by condensation with appropriate acid chlorides (benzoyl chloride, butyryl chloride, and ethyl chlorooxoacetate). The aliphatic acid chloride-based annulation reaction is new to subporphyrinoid chemistry. The phenyl (6a)- or n-propyl (6b)-substituted derivatives could be oxidized to the corresponding B­(III)­subporphyrins upon refluxing with DDQ, whereas the triethoxycarbonyl moiety (6c) was found to be resistant to oxidation and exhibits the most red-shifted absorption (587 nm) and emission (604 nm). The study indicates that absorption and emission behaviors of the B­(III)­subchlorin can be tuned by the introduction of electron-rich or electron-deficient substituents at the meso-position. B­(III)­subchlorins 6a and 6c generate singlet oxygen efficiently (44 and 40%, respectively) and, thus, may find application as potential photosensitizers in photodynamic therapy (PDT).