title: Synthesis of meso-pyrrole-substituted 22-oxacorroles by a "3+2" approach.
abstract: 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.
authors.affiliation: Department of Chemistry, Indian Institute of Technology, Powai, Mumbai 400076 (India).
authors.forename: Hemanta
authors.initials: H
authors.lastname: Kalita
authors.forename: Dhrubajyoti
authors.initials: D
authors.lastname: Kalita
authors.forename: Way-Zen
authors.initials: WZ
authors.lastname: Lee
authors.forename: Jayesh
authors.initials: J
authors.lastname: Bellare
authors.forename: Mangalampalli
authors.initials: M
authors.lastname: Ravikanth
keywords: ABC-type corroles; UV/Vis spectroscopy; biocompatible; fluorescent probes; pyrrolyl-22-oxacorroles