A catalytic versus stoichiometric photoinduced electron transfer promoted selective C16C21 bond cleavage of catharanthine
摘要:
A clean and efficient access to the cleavamine skeleton is described through the selective oxidative C-16-C-21 bond cleavage of catharanthine. The best result is obtained by the use of catalytic quantities of beta -lapachone as photosensitizer. which permits the successful control of competition between the back electron transfer. the deprotonation and the fragmentation pathway. (C) 2001 Elsevier Science Ltd. All rights reserved.
Straightforward access to anhydrovinblastine starting from the parent alkaloid leurosine is reported. The key deoxygenation step was first optimized on a model substrate. However, applied to leurosine, only the low-valent Cp2TiCl gave satisfactory results.
Synthesis of (−)-Pseudotabersonine, (−)-Pseudovincadifformine, and (+)-Coronaridine Enabled by Photoredox Catalysis in Flow
作者:Joel W. Beatty、Corey R. J. Stephenson
DOI:10.1021/ja506170g
日期:2014.7.23
Natural product modification with photo-redox catalysis allows for mild, chemoselective access to a wide array of related structures in complex areas of chemical space, providing the possibility for novel structural motifs as well as useful quantities of less abundant congeners. While amine additives have been used extensively as stoichiometric electron donors for photocatalysis, the controlled modification of amine substrates through single-electron oxidation is ideal for the synthesis and modification of alkaloids. Here, we report the conversion of the amine (+)-catharanthine into the natural products (-)-pseudotabersonine, (-)-pseudovincadifformine, and (+)-coronaridine utilizing visible light photoredox catalysis.