C-O Ring Construction: Coriolide (Fernandes), Monocillin VII (Mohapatra), Diplobifuranylone B (Zhang), Diocolletines A (Kuwahara), Griseusin A (Thorson/She), Galanthamine (Zhang/Tu)

Rodney A. Fernandes of the Indian Institute of Technology Bombay prepared coriolide (2) by Yamaguchi cyclization of the enantiomerically-enriched precursor 1. Mitsunobu cyclization of 1 (not illustrated here) efficiently delivered the opposite enantiomer (Chem. Asian J. 2019, 14, 2278. ).

Debendra K. Mohapatra of the Indian Institute of Chemical Technology showed that preforming the cobalt carbonyl complex of 3 promoted cyclization to the macrolactone 4. In the course of this synthesis, the structure of the target natural product monocillin VII (5) was corrected to that shown (Org. Lett. 2019, 21, 5952. ).

En route to diplobifuranylone B (8), Liming Zhang of the University of California, Santa Barbara used an enantioselective gold catalyst to control the relative configuration in the cyclization of 6 to the 2,5-dihydrofuran 7. This synthesis also led to the correction of the structure of the natural product (J. Org Chem. 2019, 84, 11054. ).

Diocolletines A (11), isolated from the Chinese perennial vine Dioscorea collettii, shows modest anti-cancer activity. Shigefumi Kuwahara of Tohoku University assembled 11 by adding phenyl lithium to 9, then cyclizing that product with dihydroxyacetone 10 (Org. Lett. 2019, 21, 10099. ).

The Streptomyces griseus-produced griseusins, exemplified by griseusin A (15), have interesting anti-cancer activity. Jon S. Thorson and Qing-Bai She of the University of Kentucky prepared a wide range of griseusins, including 15, based on the oxidative cyclization of 12 with 13 to give 14 (Angew. Chem. Int. Ed. 2015, 54, 11219, ; Chem. Sci. 2019, 10, 7641, ).

Galanthamine (18), isolated from the snowdrop Galanthus nivalis of Europe and southwest Asia, is used clinically in the treatment of dementia. Fu-Min Zhang and Yong-Qiang Tu of Lanzhou University developed a route to 18 centered on the organocatalyzed cyclization of 16 followed by acid treatment to give 17 (Nature Commun. 2019, 10, 2507, ; J. Org. Chem. 2019, 84, 12664, ).