Oxidation: The Kobayashi/Ito Synthesis of Isolinearol

Kazunori Miyamoto and Masanobu Uchiyama of the University of Tokyo used fluorescent light to promote the conversion of the carboxylic acid 1 into the tertiary bromide 2 (Org. Process Res. Dev. 2020, 24, 1328. DOI: 10.1021/acs.oprd.0c00130). Lukas J. Gooßen of Ruhr-Universität Bochum employed electrolysis to effect the decarboxylative coupling of the carboxylic acid 3 with 1-hydroxybenzotriazole (4), leading to the ether 5 (Nature Commun. 2020, 11, 4407. DOI: 10.1038/s41467-020-18275-1). Alejandro Baeza of the Universidad de Alicante oxidized the imine 6 to the formamide 7 (J. Org. Chem. 2020, 85, 11072. DOI: 10.1021/acs.joc.0c01579). Shinji Harada of Chiba University found that blue LEDs promoted the allylic oxidation of the alkene 8 to the enone 9 (Synlett 2020, 31, 1372. DOI: 10.1055/s-0040-1707150).

Andreas Kirschning of the Leibniz Universität Hannover used an ion exchange resin loaded with iodine azide to selectively oxidize the diol 10 to the hydroxy ketone 11 (Angew. Chem. Int. Ed. 2020, 59, 12376. DOI: 10.1002/anie.202003079). Elena Lenci and Andrea Trabocchi of the University of Florence reported the complementary oxidation of a diol to the hydroxy aldehyde (not illustrated) (Eur. J. Org. Chem. 2020, 4227. DOI: 10.1002/ejoc.202000600). David Milstein of the Weizmann Institute of Science devised a Ru catalyst that effected the direct conversion of the primary amine 12 to the carboxylic acid 13, with evolution of H₂ (J. Am. Chem. Soc. 2020, 142, 20875. DOI: 10.1021/jacs.0c10826). Professor Milstein used a closely-related Ru catalyst to couple the primary alcohol 14 with the mercaptan 15, leading to the thioester 16 (Nature Catal. 2020, 3, 887. DOI: 10.1038/s41929-020-00514-9). Jie Wu of the National University of Singapore prepared the gem iodo bromide 18 by the oxidative cleavage of the bromohydrin derived from the alkene 17 (Nature Commun. 2020, 11, 4462. DOI: 10.1038/s41467-020-18274-2).

Sukbok Chang and Sangwon Seo of KAIST devised the cleavage of the amine 19 to the bromo formamide 20 (Nature Commun. 2020, 11, 4761. DOI: 10.1038/s41467-020-18557-8). Lianyue Wang, Shuang Gao and Wen Dai of the Dalian Institute of Chemical Physics observed that the oxidative degradation of primary alcohols stopped at a branch point, so 21 was converted to the ester 22 (Angew. Chem. Int. Ed. 2020, 59, 19268. DOI: 10.1002/anie.202008261). Aitao Li of Hubei University devised an enzyme system that oxidized the hydrocarbon cyclohexane 23 to the C-6 diacid 24 (Nature Commun. 2020, 11, 5035. DOI: 10.1038/s41467-020-18833-7). Saihu Liao of Fuzhou University used visible light and the thioamide 26 to convert the active ester 25 to the mercaptan 27, with the loss of CO₂ (Nature Commun. 2020, 11, 5340. DOI: 10.1038/s41467-020-19195-w).

Isolinearol (31), isolated from the marine brown alga Dictyota cervicornis, inhibited the hemolysis and proteolysis caused by the venom of the pit viper Bothrops jararaca. In the end game of a synthesis of 31, Toyoharu Kobayashi and Hisanaka Ito of the Tokyo University of Pharmacy and Life Sciences selectively converted the terminal vinyl group of 28 into the aldehyde of 30 by cross metathesis with the vinyl boronate 29 followed by gentle oxidation (Org. Biomol. Chem. 2020, 18, 7316. DOI: 10.1039/D0OB01430C).

We note the passing of Professor Robert K. Boeckman, Jr., a distinguished contributor to our field.