Diels-Alder Cycloaddition: Pericoannosin A (Lindsley), Arborone (Corey), Furoerioaustralasine (George), Liangshanin G (Ma), Arcutinidine (Sarpong), Mitrephorone A (Magauer)
Pericoannosin A (4), produced by the endophytic fungus Periconia sp. F-31, shows moderate anti-HIV activity. Craig W. Lindsley of Vanderbilt University set the absolute configuration of intermediate 3 by the addition of 1 to 2, catalyzed by the perchlorate salt of a diaryl prolinol (J. Org. Chem. 2019, 84, 12187. ).
In 2006, E. J. Corey of Harvard University reported that a diarylprolinol triflimide salt catalyzed the enantioselective addition of 6 to just one enantiomer of racemic 5, leading to 7, that was carried on to the valuable perfume component arborone (8). Remarkably, this facile construction of an array of cyclic stereogenic centers has been little used since that time (J. Am. Chem. Soc. 2006, 128, 1346. ).
Furoerioaustralasine (11) was isolated from the flowering plant Eriostemon banksii. En route to the synthesis of 11, in the process correcting the structure to that shown, Jonathan H. George of the University of Adelaide cyclized 9 to 10 (Org. Lett. 2019, 21, 8776. ).
Liangshanin G (15) was isolated from the Chinese medicinal herb Rabdosia liangshanica. Dawei Ma of the Shanghai Institute of Organic Chemistry assembled the tricyclic core 14 of 15 by adding the bridgehead enone derived from 13 to the diene 12 (Angew. Chem. Int. Ed. 2019, 58, 15731. ).
Arcutinidine (19) was isolated from Aconitum arcuatum Maxim. (Ranunculaceae) of Manchuria. Richmond Sarpong of the University of California, Berkeley, assembled the key intermediate 18 by oxidizing 16 in the presence of acrylic acid 17 (J. Am. Chem. Soc. 2019, 141, 13713. ).
The oxetane-containing mitrephorone A (22), isolated from the Bornean shrub Mitrephora glabra, shows both antimicrobial activity and cytotoxicity. Thomas Magauer of the Leopold-Franzens-University Innsbruck prepared 21 by the internal Diels-Alder cyclization of 20 (J. Am. Chem. Soc. 2019, 141, 19589. ).