C-O Ring Construction: Phyllostictine A (Shipman), Kujuonin A2 (Rychnovsky), Ivorenolide B (Mohapatra), Asimicin (Inoue), Paecilomycin B (Ohba), Phomactin A (Du/Lee)
Michael Shipman of the University of Warwick showed that on exposure to base, 1 cyclized to the dihydropyran 2. This established the central ring system of phyllostictine A (3) (Chem. Commun. 2018, 54, 7211. DOI: 10.1039/C8CC03349H).
Ascorbic acid (4) is a commodity chemical. Scott D. Rychnovsky of the University of California Irvine established that 4 could act as a nucleophile in a Tsuji-Trost coupling with 5, assembling 6 with high diastereocontrol. Ozonolysis of 6 led to kujounin A2 (7) (Org. Lett. 2018, 20, 5849. DOI: 10.1021/acs.orglett.8b02530).
Debendra K. Mohapatra of the Indian Institute of Chemical Technology constructed the macrolactone 9 by the intramolecular oxidative of 8. Diastereoselective epoxidation completed the synthesis of ivorenolide B (10) (Eur. J. Org. Chem. 2018, 4376. DOI: 10.1002/ejoc.201800708).
With the exception of the venerable Kolbe electrolysis, radical-radical coupling has not usually been an effective synthetic strategy. That situation is changing, as illustrated by the synthesis of asimicin (13) by Masayuki Inoue of the University of Tokyo. A key step in the synthesis was the oxidative dimerization of 11 to 12 (Chem. Eur. J. 2018, 24, 18907. DOI: 10.1002/chem.201805317).
Kiyomi Ohba of the Mitsubishi Tanaba Pharma Corporation assembled 16 by adding 15 to the lactone 14. Reduction followed by macrolactone construction completed the synthesis of paecilomycin B (17) (J. Org. Chem. 2018, 83, 7019. DOI: 10.1021/acs.joc.7b03041).
Phomactin A (21) is a potent antagonist of platelet activating factor. En route to 21, Guangyan Du of Peking University Shenzen Graduate School and Chi-Sing Lee of Hong Kong Baptist University effected the coupling of 18 with 19, leading to 20 (Org. Lett. 2018, 20, 7466. DOI: 10.1021/acs.orglett.8b03242).