title: De novo synthesis of long-wavelength absorbing chlorin-13,15-dicarboximides.
abstract: Chlorins bearing a six-membered imide ring spanning positions 13-15, commonly referred to as purpurinimides, exhibit long-wavelength absorption yet have heretofore only been available via semisynthesis from naturally occurring chlorophylls. A concise route to synthetic chlorins, which bear a geminal dimethyl group in the pyrroline ring, has been extended to provide access to chlorin-13,15-dicarboximides. The new route entails (i) synthesis of a 13-bromochlorin, (ii) palladium-catalyzed carbamoylation at the 13-position, (iii) regioselective 15-bromination under acidic conditions, and (iv) one-flask palladium-mediated carbonylation and ring closure to form the imide. In some cases the ring closure reaction afforded the isomeric (and readily separable) chlorin-isoimide in addition to the chlorin-imide. The resulting chlorin-imides and chlorin-isoimides exhibit long-wavelength absorption (679-715 nm) and emission (683-720 nm) in the far-red and near-infrared spectral region. The absorption of the chlorin-(iso)imides fills the spectral window between that of analogous synthetic chlorins and 13(1)-oxophorbines (603-687 nm) and bacteriochlorins (707-792 nm). The synthetic versatility of the de novo route complements the existing semisynthetic route from chlorophylls and should enable fundamental spectroscopic studies and photochemical applications.
authors.affiliation: Department of Chemistry, North Carolina State University, Raleigh, North Carolina 27695-8204, USA.
authors.forename: Marcin
authors.initials: M
authors.lastname: Ptaszek
authors.forename: Dorothée
authors.initials: D
authors.lastname: Lahaye
authors.forename: Michael
authors.initials: M
authors.lastname: Krayer
authors.forename: Chinnasamy
authors.initials: C
authors.lastname: Muthiah
authors.forename: Jonathan S
authors.initials: JS
authors.lastname: Lindsey