Department of Chemistry, North Carolina State University, Raleigh, North Carolina 27695-8204, USA.
J Org Chem. 2010 Mar 5;75(5):1659-73. doi: 10.1021/jo902649d.
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.
带有跨越 13-15 位的六元酰亚胺环的叶绿素，通常被称为紫质酰胺，具有长波长吸收，但迄今为止仅可通过天然叶绿素的半合成获得。一种简洁的合成叶绿素方法，即在吡咯啉环上带有偕二甲基基团，已被扩展到合成叶绿素-13,15-二羧酸酰胺。新路线需要（i）合成 13-溴叶绿素，（ii）钯催化在 13 位的氨甲酰化，（iii）在酸性条件下区域选择性 15-溴化，以及（iv）一锅钯介导的羰基化和环化形成酰亚胺。在某些情况下，环合反应除了生成叶绿素酰亚胺外，还生成了异构（且易于分离）的叶绿素异酰亚胺。所得的叶绿素酰亚胺和叶绿素异酰亚胺在远红和近红外光谱区域表现出长波长吸收（679-715nm）和发射（683-720nm）。叶绿素-（异）酰亚胺的吸收填补了类似合成叶绿素和 13（1）-氧代胆色素（603-687nm）和细菌叶绿素（707-792nm）之间的光谱窗口。从头合成路线的合成多功能性补充了现有从叶绿素的半合成路线，应能实现基础光谱研究和光化学应用。
