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Monday, March 8, 2021
Douglass F. Taber
University of Delaware

Functional Group Interconversion: The Xu/Li Synthesis of Prostratin

Steven T. Diver of the University at Buffalo observed high geometric control in the Co-catalyzed conversion of the diene 1 to the diene 2 (Org. Lett. 2020, 22, 750. ). Agustí Lledós of the Universitat Autňnoma de Barcelona and Antoni Riera of the Barcelona Institute of Science and Technology rearranged the oxetane 3 to the homoallylic alcohol 4 (Angew. Chem. Int. Ed. 2020, 59, 7521. ). Zhenghu Xu of Shandong University converted the azido alkene 5 into the ketone 6 (Nature Commun. 2020, 10, 3158. ). Hongbin Zhang and Xiaodong Yang of Yunnan University prepared the diene 8 by exposing the propargyl ether 7 to strong base (Eur. J. Org. Chem. 2020, 483. ). Tomas Hudlicky of Brock University showed that the N-oxide derived from 9 smoothly eliminated to the alkene 10 (J. Am. Chem. Soc. 2019, 141, 10883. ). Under Mitsunobu conditions but without an added nucleophile, Hanfeng Ding of Zhejiang University demonstrated that the equatorial alcohol 11 could be dehydrated to the alkene 12 (Org. Lett. 2020, 22, 1426. ).

Professor Zhang and Jingbo Chen, also of Yunnan University, observed that neat with catalytic acetic acid, the amine 14 smoothly opened the epoxide 13, leading to the amino alcohol 15 (Chem. Commun. 2020, 56, 2256. ). Ruzhang Liu of Yangzhou University established that the azide 16, an equilibrating mixture of allylic regioisomers, could be hydrosilylated to 17 (Chem. Commun. 2020, 56, 5038. ).

Teresa Martínez del Campo and Israel Fernández of the Universidad Complutense de Madrid and Pedro Almendros of IQOG prepared the enone 19 by the Se-mediated rearrangement of 18, presumably in the presence of adventitious water (Org. Lett. 2020, 22, 3979. ). Wen Yang and Wanxiang Zhao of Hunan University showed that Rh-mediated alkene migration could be used to convert the alkenyl alcohol 20 to the ketone 21 (Org. Lett. 2020, 22, 1265. ).

The conversion of the carboxylic acid 22 to the nitro alkane 24 developed by Ryosuke Matsubara of Kobe University proceeded in two steps, decarboxylative radical addition to the furoxan 23, followed by reduction (Org. Lett. 2020, 22, 1182. ). Ze-Feng Xu and Chuan-Ying Li of Zhejiang Sci-Tech University used tosyl azide to convert the alkyne 25 to the cyano sulfone 26 (Org. Chem. Front. 2020, 7, 596. ).

In the last stage of a synthesis of prostratin 29, Liang Xu of Shihezi University and Pengfei Li of Xi'an Jiaotong University used a Rh catalyst to equilibrate the exomethylene ketone 27 to the enone 28 (J. Org. Chem. 2020, 85, 4813. ). Although the endocyclic alkene is usually more stable that the exocyclic alkene, as here, that is not always the case, and it is prudent to support with computational analysis a plan for such an equilibration (Tetrahedron Lett. 1993, 34, 2243. ).

D. F. Taber, Org. Chem. Highlights 2021, March 1.