C-O Ring Construction: Sesamin (Zhang), TAN-2483B (Harvey), Regalamine (Xie/Zhou), Laurefurenyne D (Burton), Phyllanemblinin B (Wakamori), Leonuketal (Grant/Furkert/Brimble)
Yong Jian Zhang of Shanghai Jiao Tong University established the enantioselective Pd-catalyzed coupling of 1 with 2, leading to 3. The tetrahydrofuran 3 was readily carried on to the furofuran lignan sesamin (4) (Chem. Commun. 2020, 56, 12431. ).
The furo[3,4-b]pyran-5-one TAN-2483B (7), isolated from a fungal fermentation, showed antibacterial and anti-inflammatory activity. En route to 7, Joanne E. Harvey of the Victoria University of Wellington devised the ring expansion of the dihydrofuran 5 to the dihydropyran 6 (Org. Lett. 2020, 22, 9427. ).
Regalamine (10) is a homoproaphorphine alkaloid isolated from the Eurasian lily Colchicum kesselringii. Jian-Hua Xie and Qi-Lin Zhou of Nankai University established the central ring system of 10 by the oxidative rearrangement of 8 to 9 (Org. Lett. 2020, 22, 7526. ).
Jonathan W. Burton of the University of Oxford established a general route to the Laurencia natural products, based on the rearrangement of 11 to 12. In the course of this work, he corrected the structures of several of them, including laurefurenyne D (13) (Chem. Sci. 2020, 11, 11592. ).
The juice of the fruit of the Malacca tree, Phyllanthus emblica, has been used as an anti-inflammatory and antipyretic agent. In the course of a synthesis of the ellagitannin phyllanemblinin B (16), isolated from that juice, Shinnosuke Wakamori of Kansei Gakuin University observed high diastereoselectivity in the oxidative conversion of 14 to the biphenyl 15 (Synlett 2020, 31, 1389, ; Chem. Eur. J. 2020, 26, 16408, ).
Leonuketal (19), isolated from the Chinese liverwort Leonurus japonicus, showed significant vasorelaxant activity. Phillip S. Grant, Daniel P. Furkert, and Margaret A. Brimble of the University of Auckland demonstrated that the enol 17 could directly participate in the gold-mediated cyclization, leading to the spiroketal 18 (Org. Lett. 2020, 22, 8735. ).