Other Methods for Carbocyclic Construction: Aspidodispermine (Heretsch), Lepadiformine A (Tokuyama), Farnesin (Gao), Ganocin B (Zhao), Dankasterone B (Heretsch), Canataxpropellane (Gaich)
The Ramberg-Bäcklund alkene construction is usually carried out on sulfones. In the course of a synthesis of aspidodispermine (3), Philipp Heretsch of the Freie Universität Berlin showed that the preparation of the cyclobutene 2 was better carried out starting with the sulfoxide 1 (Org. Lett. 2020, 22, 3956. ).
Lepadiformine A (6), isolated from the marine tunicate Clavelina lepidaformis, is a cardiac K+-channel blocker. A key step in the route to 6 devised by Hidetoshi Tokuyama of Tohoku University was the reductive radical cyclization of 4 to 5 (Org. Lett. 2020, 22, 3313. ).
Farnesin (9) was isolated from the seeds of Acacia farnesiana. En route to 9, Shuanhu Gao of East China Normal University prepared the key cyclopentanone 8 by the photochemical Nazarov cyclization of 7 (Angew. Chem. Int. Ed. 2020, 59, 7444. ).
Ganocin B (12) was isolated from the fruiting bodies of Ganoderma cochlear, a famous medicinal mushroom of China. Yu-Ming Zhao of Shaanxi Normal University assembled almost the entire structure of 12 by the cyclization of 10 to 11 (Angew. Chem. Int. Ed. 2020, 59, 7419. ).
Dankasterone B (15), isolated from the sponge-derived fungus Gymnascella dankaliensis, has a massively rearranged steroid skeleton. Professor Heretsch replicated this rearrangement, oxidizing 13, then reducing the α-iodo ketone so produced to deliver 14 (J. Am. Chem. Soc. 2020, 142, 104. ).
Canataxpropellane (18), isolated from Taxus canadensis, has a particularly challenging carbon skeleton. Tanja Gaich of the University of Konstanz assembled 18 via the photochemical cyclization of 16 to 17 (Science 2020, 367, 676. ).
We note with regret the passing of our friend and colleague Victor Snieckus, 1937-2020.