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. ).
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. ).
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. ).
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. ).
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. ).
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. ).