Oxidation: The Mander/Lan Synthesis of Gibberellin A₂₄

Ilfir R. Ramazanov of the Institute of Petrochemistry and Catalysis of the Russsian Academy of Sciences oxidized the amine 1 to the ketone 2 (Synlett 2018, 29, 1191. DOI: 10.1055/s-0037-1609336). Frank Glorius of the Westfälische Wilhelms-Universität Münster effected decarboxylation of 3 to 4 (ACS Catal. 2018, 8, 1715. DOI: 10.1021/acscatal.7b04281). Yuanzhi Xia of Wenzhou University demonstrated that heating in formamide (6) converted the hydroxamic acid 5 into 7 (Org. Biomol. Chem. 2018, 16, 3615. DOI: 10.1039/C8OB00490K). Feng Xu and Yong-Li Zhong of Merck Process developed a practical protocol using the diamine 9 for converting an alkene 8 into the alkyne 10 (Org. Lett. 2017, 19, 5880. DOI: 10.1021/acs.orglett.7b02867).

Zhihai Ke and Ying-Yeung Yeung of the Chinese University of Hong Kong observed high regioselectivity in the oxidative cleavage of the cyclopropane 11 to the diol 12 (Angew. Chem. Int. Ed. 2018, 57, 3782. DOI: 10.1002/anie.201713422). Timothy R. Newhouse of Yale University developed a simple procedure using 14 for converting a cyclic ketone 13 to the cyclohexenone 15 (Org. Lett. 2018, 20, 684. DOI: 10.1021/acs.orglett.7b03818). Thomas Maguer of the Ludwig-Maximilians-University, Munich effected the β-bromination of the enone 16, leading to 17 (J. Org. Chem. 2017, 82, 7410. DOI: 10.1021/acs.joc.7b01095). Alex M. Szpilman of Ariel University oxidized the enol ether 18 with Koser's reagent (19), then coupled the intermediate with TMS-N₃ to give the α-azido ketone 20 (J. Org. Chem. 2018, 83, 2442. DOI: 10.1021/acs.joc.7b03058). K. Rajender Reddy of the Indian Institute of Technology Tarnaka reported a related procedure for converting a ketone to the α-phenoxy ketone (not illustrated) (Tetrahedron Lett. 2018, 59, 33. DOI: 10.1016/j.tetlet.2017.11.043).

Ritwika Ray, Debabrata Maiti and Goutam Kumar Lahiri of the Indian Institute of Technology Bombay oxidized the primary amine 21 to the amide 22 (Chem. Eur. J. 2018, 24, 1067. DOI: 10.1002/chem.201705601). Martin J. Lear of the University of Lincoln and Yujiro Hayashi of Tohoku University converted the nitro group of 23 to the ester 24 (Chem. Commun. 2018, 54, 6360. DOI: 10.1039/C8CC03191F). Chao-Jun Li of McGill University showed that Ag triflate was an effective catalyst for the oxidative cleavage of the diol 25 to the diacid 26 (Angew. Chem. Int. Ed. 2018, 57, 2616. DOI: 10.1002/anie.201711531). Keiji Maruoka of Kyoto University coupled the intermediate from cleavage of the silyl peroxide 27 with 28, leading to the alkyne 29 (Org. Lett. 2018, 20, 1400. DOI: 10.1021/acs.orglett.8b00173).

The gibberellins, including the commercial gibberellin A₃, are well known as plant growth regulators. Toward the end of the chemical conversion of GA₃ to GA₂₄ (32), Lewis N. Mander of the Australian National University and Ping Lan of Jinan University oxidized the ketone 30 to the aldehyde 31. Saponification then completed the synthesis of 32 (J. Org. Chem. 2018, 83, 6566. DOI: 10.1021/acs.joc.8b00876).