C-H Functionalization: The Zhu Synthesis of β-Cuparenone

Soon Hyeok Hong of KAIST devised the photochemically-promoted coupling of the acid chloride 2 with the hydrocarbon 1, leading to the ketone 3 as a mixture of diastereomers (Nature Commun. 2022, 13, 5200. DOI: 10.1038/s41467-022-32851-7). Devarajulu Sureshkumar of the Indian Institute of Science Education and Research Kolkata developed the diastereoselective preparation of the protected α-amino acid 6 by the coupling of the amide 4 with iodoacetonitrile 5 (Chem. Commun. 2022, 58, 7793. DOI: 10.1039/D2CC03106J). Zhiqiang Pan and Chengfeng Xia of Yunnan University observed high regioselectivity in the acetylation of trans-decalin (7) with the phenylsulfonyl ethanone oxime 8, leading after hydrolysis to the ketone 9 (Org. Lett. 2022, 24, 7983. DOI: 10.1021/acs.orglett.2c03142). Jian Liu and Xiaolei Wang of Lanzhou University achieved high site selectivity in the preparation of the polyol 12 by coupling myo-inositol 10 with styrene 8 (Chem. Commun. 2022, 58, 9934. DOI: 10.1039/D2CC03569C).

Hidetoshi Noda and Masakatsu Shibasaki of the Institute of Microbial Chemistry also achieved high diastereoselectivity in the cyclization of the isoxazolidin-5-one 13 to the pyrrolidine 14 (Angew. Chem. Int. Ed. 2022, 61, e202212421. DOI: 10.1002/anie.202212421). Xin Sun and Miao Yu of Huanghuai University and Ji-Kai Liu and Bin Wu of the South-Central University for Nationalities effected the photochemically-promoted cyclization of the allyl cinnamate 15 to the lactone 16 (Org. Chem. Front. 2022, 9, 2316. DOI: 10.1039/D1QO01952J). Josep M. Luis and Miquel Costas of the Universitat de Girona and Massimo Bietti of the Università "Tor Vergata" showed that by choice of catalyst, either methyl group of ketopinic acid (17) could be oxidized to the lactone, 18 or its regioisomer (J. Am. Chem. Soc. 2022, 144, 19542. DOI: 10.1021/jacs.2c08620). Lung Wa Chung of the Southern University of Science and Technology and Zheng Huang of SIOC achieved remarkable regioselectivity in the conversion of the silane 19 to the cyclic silane 21, with t-butyl ethylene 20 as the H₂ acceptor (J. Am. Chem. Soc. 2022, 144, 20903. DOI: 10.1021/jacs.2c09356).

The Rh-catalyzed cyclization of the oxime tosylate 22 to the cyclopropane 23 developed by Sailu Munnuri of the UT Southwestern Medical Center is thought to proceed by hydride abstraction followed by recombination (J. Am. Chem. Soc. 2022, 144, 17989. DOI: 10.1021/jacs.2c07427). The cyclization of the oxime aldehyde 24 to the cyclobutanol 25 devised by Fabrizio Vetica and Patrizia Gentili of the Sapienza University of Rome proceeds by H-atom abstraction/recombination (J. Org. Chem. 2022, 87, 13803. DOI: 10.1021/acs.joc.2c01503). Lin Guo and Wujiong Xia of the Harbin Institute of Techology used a similar strategy to assemble 28 by coupling the alkyne 26 with the α-keto acid 27 (Org. Chem. Front. 2022, 9, 6513. DOI: 10.1039/D2QO01424F). Matthew S. Sigman of the University of Utah and K. N. Houk and Hosea M. Nelson of UCLA achieved appreciable enantioselectivity in the imidodiphosphorimidate-catalyzed cyclization, mediated by the allyl silane 30, of the enol tosylate 29 to the bicyclic alkene 31 (Science 2022, 378, 1085. DOI: 10.1126/science.ade5320).

Gangguo Zhu of Zhejiang Normal University devised a concise synthesis of β-cuparenone (35), based on the coupling of the aldehyde 32 with the chloroalkyne 33 to give 34. Cyclopentanone formation proceeds by initial formation of the acyl radical, that adds regioselectively to the alkyne. The resulting alkenyl radical abstracts an H-atom to give the tertiary radical, that then adds in a conjugate sense to the enone, to give 34 (Nature Commun. 2022, 13, 4734. DOI: 10.1038/s41467-022-32467-x).