Synthesis of meso-Pyrrole-Substituted 22-Oxacorroles by a "3+2" Approach

• Published in: Chemistry : a European journal Vol. 20; no. 33; pp. 10404 - 10413
• Main Authors: Kalita, Hemanta, Kalita, Dhrubajyoti, Lee, Way-Zen, Bellare, Jayesh, Ravikanth, Mangalampalli
• Format: Journal Article
• Language: English
• Published: Weinheim WILEY-VCH Verlag 11.08.2014; WILEY‐VCH Verlag; Wiley; Wiley Subscription Services, Inc
• Subjects: ABC-type corroles; Aromatic compounds; Biocompatibility; biocompatible; Biological; Chemistry; Chemistry, Multidisciplinary; Condensing; Equivalence; Fluorescence; fluorescent probes; Maxima; Oxidation; Physical Sciences; pyrrolyl-22-oxacorroles; Science & Technology; UV/Vis spectroscopy; UV; SMARAGDYRINS; 1ST EXAMPLES; biocompatible; CONDENSATION; Vis spectroscopy; pyrrolyl-22-oxacorroles; DIPYRROMETHANES; ABC-type corroles; fluorescent probes; CORE-MODIFIED CORROLES; UV/Vis spectroscopy
• ISSN: 0947-6539; 1521-3765
• DOI: 10.1002/chem.201402710

Unsymmetrical 22‐oxacorrole containing two aryl groups and one pyrrole group at the meso position was synthesized by condensing one equivalent of 16‐oxatripyrrane with one equivalent of meso aryl dipyromethane under mild acid‐catalyzed conditions followed by oxidation with 2,3‐dichloro‐5,6‐dicyano‐1,4‐benzoquinone (DDQ). This [3+2] condensation approach was expected to yield meso‐free 25‐oxasmaragdyrin but unexpectedly afforded unsymmetrical meso‐pyrrole‐substituted 22‐oxacorrole. We demonstrated the versatility of the reaction by synthesizing four new meso‐pyrrole‐substituted 22‐oxacorroles. The reactivity of α‐position of meso‐pyrrole was tested by carrying out various functionalization reactions such as bromination, formylation, and nitration and obtained the functionalized meso‐pyrrole‐substituted 22‐oxacorroles in decent yields. The X‐ray structure obtained for one of the functionalized meso‐pyrrole substituted 22‐oxacorrole revealed that the macrocycle was nearly planar and the meso‐pyrrole was in the perpendicular orientation with respect to the macrocyclic plane. The meso‐pyrrole‐substituted 22‐oxacorroles absorb strongly in 400–700 nm region with one strong Soret band and four weak Q bands. The 22‐oxacorroles are strongly fluorescent and showed emission maxima at ≈650 nm with decent quantum yields and singlet‐state lifetimes. The 22‐oxacorroles are redox‐active and exhibited three irreversible oxidations and one or two reversible reduction(s). A preliminary biological study indicated that meso‐pyrrole corroles are biocompatible. Mastering ABCorroles: Syntheses of the first examples of stable fluorescent meso‐pyrrole‐substituted 22‐oxacorroles are described (see scheme; TFA=trifluoroacetic acid; DDQ=2,3‐dichloro‐5,6‐dicyano‐1,4‐benzoquinone). A preliminary biological study indicated that meso‐pyrrole corroles are biocompatible.