Oxidation: The Micalizio Route to the Corialactones
Bo Xu of Donghua University and Gerald B. Hammond of the University of Louisville converted the aldehyde 1 into the corresponding dihydropyridine, and thus to the bromide 2 (Org. Lett. 2019, 21, 3848. ). Erick M. Carreira of ETH Zürich used the amide of 3 to direct the iodination to 4 (J. Am. Chem. Soc. 2019, 141, 8758. ). Burkhard König of the Universität Regensburg effected the conversion of the carboxylic acid 5 to 7 (Chem. Commun. 2019, 55, 3489. ). Almost forty years ago, Jiro Tsuji, then at the Tokyo Institute of Technology, reported the conversion of 8 to 9 (J. Am. Chem. Soc. 1982, 104, 5844. ). This is still one of the more convenient methods for preparing low molecular weight cyclic enone starting materials.
Matthew D. Shair of Harvard University oxidized the alkenyl triflate 10 to the versatile enone 11 (Org. Lett. 2019, 21, 2473. ). Kevin Lam of the University of Greenwich prepared the mixed acetal 13 from the acid 12 (Chem. Commun. 2018, 54, 9969. ). Wei Yu of Lanzhou University assembled the mixed aminal 15 by cyclization of the azide 14 (Org. Lett. 2019, 21, 1559. ). László Kürti of Rice University prepared the amino ketone 17 by amination of the silyl enol ether 16 (J. Am. Chem. Soc. 2019, 141, 2242. ). Kensuke Kiyokawa and Satoshi Minakata of Osaka University reported a related amination of ketene silyl acetals (Angew. Chem. Int. Ed. 2019, 58, 8907. ).
Jian Wang of Tsinghua University used an NHC catalyst to oxidize the aldehyde 18 to the ester 19 (Org. Chem. Front. 2019, 6, 688. ). David Milstein of the Weizmann Institute of Science devised a Mn catalyst for the direct conversion of the alcohol 20 to the methyl ester 21 (ACS Catal. 2019, 9, 479. ). Bing Sun and Hua-Li Qin of the Wuhan University of Technology oxidized the alcohol 22 to the nitrile 23 (Eur. J. Org. Chem. 2019, 3190. ). Yan He and Xuesen Fan of Henan Normal University showed that 2,2,6,6-tetramethyl-1-oxopiperidin-1-ium tetrafluoroborate was an effective catalyst for the oxidative cleavage of 24 to 25 (Org. Lett. 2019, 21, 1676. ).
The corialactones, exemplified by corialactone D (29), isolated from the Himalayan shrub Coriaria nepalensis, are noted for their ability to enhance neurite outgrowth. En route to 28, a ubiquitous intermediate for the preparation of this class of natural products, Arti B. Gaur and Glenn A. Micalizio of Dartmouth College oxidized the silyl diene 26 to the enone 27 (Org. Lett. 2019, 21, 3193. ). Notably, some of the derivatives that they prepared inhibited neurite outgrowth without displaying cytotoxicity.
We note with sadness the passing of Professor James D. White of Oregon State University, whose work has been featured in these pages.