C-O Ring Construction: The Jeong/Shin Syntheses of Giffonin H
Madhuri Vangala of the Indian Institute of Science Education and Research used a gold catalyst to convert 1 to the azide 2 (Beilstein J. Org. Chem. 2018, 14, 682. ). Adrien Quintard of Aix Marseille University achieved high ee in the addition of 4 to 3, leading after cyclization to the tetrahydrofuran 5 (Org. Lett. 2019, 21, 453. ). Liming Zhang of the University of California, Santa Barbara observed high diastereoselectivity in the cyclization of 6 to the 2,5-dihydrofuran 7 (J. Am. Chem. Soc. 2019, 141, 3787. ). Timothy J. Donohoe of the University of Oxford added the carbocation derived from 9 to 8, leading to 10 (J. Am. Chem. Soc. 2019, 141, 6489. ).
Olga García Mancheño of the University of Münster assembled 13 by the enantioselective addition of 12 to 11 (Angew. Chem. Int. Ed. 2019, 58, 3217. ). Shuang Yang and Xinqiang Fang of the Fujian Institute of Research on the Structure of Matter used a thiourea catalyst to mediate the addition of 15 to 14, leading to 16 (Org. Lett. 2019, 21, 1979. ). Atsushi Ueda and Masakazu Tanaka of Nagasaki University took advantage of the enantioselective addition of malonate 18 to 17, carrying the adduct on to 19 (Heterocycles 2019, 99, 989. ). Joanne E. Harvey of Victoria University of Wellington added dibromocarbene to 20, then added 21 to the rearranged adduct, leading to 22 (Chem. Asian. J. 2019, 14, 1230. ).
Yasuharu Yoshimi of the University of Fukui devised the macrocyclization of 23 to 24 (J. Org. Chem. 2019, 84, 8019. ). Hyelee Lee and Nunzio Sciammetta of Merck used a nickel catalyst and irradiation to cyclize the pentapeptide 25 to 26 (Chem. Sci. 2019, 10, 5073. ).
Bill C. Hawkins of the University of Otago alkylated 27 with 28 to give an intermediate cyclopropane, that was rearranged and deallylated to give 29 (Org. Lett. 2019, 21, 2872. ). Michael S. VanNieuwenhze of Indiana University devised the reductive Heck cyclization of 30 to 31 (J. Org. Chem. 2019, 84, 173. ).
Giffonin H (34), isolated from the common hazel Corylus avellana, shows anti-oxidant activity. Jin-Hyun Jeong of Yonsei University and Dongyun Shin of Gachon University assembled the meta /para skeleton of 34 by the fluoride-mediated cyclization of 32 to 33 (Org. Chem. Front. 2019, 6, 704. ).
The key to the cyclization was the use of an anhydrous fluoride source. An alternative approach to anhydrous fluoride is commercial TBAF in THF with solid NH4Cl added (J. Am. Chem. Soc. 1998, 120, 13285. ).