“Golden” Cascade Cyclization to Benzo[c]‐Phenanthridines

• Published in: Chemistry : a European journal 2021-10, Vol.27 (59), p.14778-14784
• Main Authors: Hendrich, Christoph M., Senn, Sebastian, Haas, Lea, Hoffmann, Marvin T., Zschieschang, Ute, Greiner, Luca C., Rominger, Frank, Rudolph, Matthias, Klauk, Hagen, Dreuw, Andreas, Hashmi, A. Stephen K.
• Format: Article
• Language: English
• Subjects: Alkynes; benzo[c]phenanthridines; benzylamines; Cascade chemical reactions; cascade reactions; Chemistry; Electronics industry; homogeneous gold catalysis; Organic semiconductors; Oxidation; Semiconductor devices; Thin film transistors
• ISSN: 0947-6539; 1521-3765
• DOI: 10.1002/chem.202102134

Herein, we describe a gold‐catalyzed cascade cyclization of Boc‐protected benzylamines bearing two tethered alkyne moieties in a domino reaction initiated by a 6‐endo‐dig cyclization. The reaction was screened intensively, and the scope was explored, resulting in nine new Boc‐protected dihydrobenzo[c]phenanthridines with yields of up to 98 %; even a π‐extension and two bidirectional approaches were successful. Furthermore, thermal cleavage of the Boc group and subsequent oxidation gave substituted benzo[c]phenanthridines in up to quantitative yields. Two bidirectional approaches under the optimized conditions were successful, and the resulting π‐extended molecules were tested as organic semiconductors in organic thin‐film transistors. Suitable substitution: The synthesis of highly substituted six‐membered N‐heterocycles using gold catalysis is reported. The applied cascade reaction using different substituted alkyne systems as starting materials furnished the corresponding benzo[c]phenanthridines in very high overall yields. In addition, two π‐extended molecules were studied as organic semiconductors in organic thin‐film transistors.