Alkaloid Synthesis: Julifloridine (Huang), γ-Lycorane (Wang/Huang), Lycojaponicumin A (Zhang/Tu), Isatindigotindoline C (Siitonen/Kürti), Curvulamine (Maimone), Kopsifoline D (Peng)
Pei-Qiang Huang of Xiamen University achieved high diastereoselectivity in the reductive coupling of 1 with 2. Hydrogenation of the product 3 directly delivered julifloridine (4) (Eur. J. Org. Chem. 2020, 52. DOI: 10.1002/ejoc.201901752).
Xiaoji Wang of Jiangxi Science and Technology Normal University showed that even in the presence of the electron-rich aromatic ring, iodination converted the amine 5 to 6. On exposure to a Pd catalyst, 6 was converted into a 1:1 mixture of γ-lycorane 7 and its regioisomer (Tetrahedron Lett. 2020, 61, 151733. DOI: 10.1016/j.tetlet.2020.151733).
Shu-Yu Zhang and Yong-Qiang Tu of Shanghai Jiao Tong University showed that the combination of 8 with hydroxylamine led, via dipolar cycloaddition followed by intramolecular N-alkylation, to the pentacyclic 9. Oxidation over several steps delivered the Lycopodium alkaloid lycojaponicumin A (10) (Org. Lett. 2020, 22, 3775. DOI: 10.1021/acs.orglett.0c00961).
Juha H. Siitonen and László Kürti of Rice University assembled 14 by combining 11, 12 and 13 in equimolar proportions. Epimerization led to isatindigotindoline C (15) (Org. Biomol. Chem. 2020, 18, 2051. DOI: 10.1039/D0OB00270D).
En route to curvulamine (18), Thomas J. Maimone of the University of California, Berkeley prepared the iodide 16. After several alternative approaches, it was found that irradiation in the presence of sodium bicarbonate led to clean conversion to 17 (J. Am. Chem. Soc. 2020, 142, 1206. DOI: 10.1021/jacs.9b12546).
The cyclization of 19 to 20 developed by Xiao-Shui Peng of the Chinese University of Hong Kong proceeded by initial conjugate addition, followed by intramolecular alkylation. Conversion of 20 to the indole then led to kopsifoline D (21) (J. Org. Chem. 2020, 85, 967. DOI: 10.1021/acs.joc.9b02918).