Metal-Mediated C-C Ring Construction: The Echavarren Synthesis of Repraesentin F

T. V. RajanBabu of Ohio State University constructed the cyclobutane 2 by adding two equivalents of ethylene to the enyne 1 (Science 2018, 361, 68. DOI: 10.1126/science.aat6205). Kazuhiko Takatori of the Meiji Pharmaceutical University cyclized 3 to the cyclobutane 4 (Tetrahedron Lett. 2018, 59, 3872. DOI: 10.1016/j.tetlet.2018.09.030).

Several strategies have emerged for the assembly of cyclic sulfones. Paolo Pasetto of AMRI used Ramberg-Bäcklund ring contraction to convert 5 to the cyclopentene 6 (Tetrahedron Lett. 2018, 59, 2797. DOI: 10.1016/j.tetlet.2018.06.014). Xavier Verdaguer and Antoni Riera of the Barcelona Institute of Science and Techology showed that kinetic rearrangement of the Pauson-Khand adduct of 7 with ethylene could be kinetically isomerized to the more stable 8 in high ee (Org. Lett. 2018, 20, 3953. DOI: 10.1021/acs.orglett.8b01525). Wen-Dao Chu, Long He and Quan-Zhong Liu of China West Normal University prepared 11 by the Rh-catalyzed addition of 9 to 10 (J. Org. Chem. 2018, 83, 12806. DOI: 10.1021/acs.joc.8b01546). Barry M. Trost of Stanford University developed the trimethylene methane addition of 13 to 12 to give 14 (Angew. Chem. Int. Ed. 2018, 57, 11025, DOI: 10.1002/anie.201805876; Org. Lett. 2018, 20, 3938, DOI: 10.1021/acs.orglett.8b01518).

Lili Lin and Xiaoming Feng of Sichuan University devised a Zn catalyst that mediated the enantioselective Diels-Alder cycloaddition of 15 with 16 to give 17 (J. Org. Chem. 2018, 83, 12527. DOI: 10.1021/acs.joc.8b01771). The cyclohexane 19 has 20 unique C-H insertion sites. Huw M. L. Davies of Emory University developed a Rh catalyst that directed insertion of 18 into just one of those, leading to 20 (Nature 2018, 564, 395. DOI: 10.1038/s41586-018-0799-2). Carlos R. D. Correia of the University of Campinas and Gerald B. Hammond of the University of Louisville added the diazonium salt 22 to the prochiral diol 21 to give 23 in high ee (Adv. Synth. Catal. 2018, 360, 3760. DOI: 10.1002/adsc.201800785). Henrik H. Jensen of Aarhus University assembled the highly-substituted cyclohexane 25 by the addition of excess vinyl magnesium bromide to the lactone 24 (Org. Biomol. Chem. 2018, 16, 6250. DOI: 10.1039/C8OB01433G).

E. J. Corey of Harvard University prepared the medium ring alcohol 28 by reducing 26 in the presence of an excess of the recoverable amino alcohol 27 (J. Am. Chem. Soc. 2018, 140, 16909. DOI: 10.1021/jacs.8b10522). William J. Kerr optimized the catalytic microwave-mediated Pauson-Khand cyclization of 29, supported by 30, leading to the tricyclic enone 31 (Tetrahedron 2018, 74, 5062. DOI: 10.1016/j.tet.2018.06.032).

The tricyclic sesquiterpene repraesentin F (34), isolated from the Japanese fungus Lactarius repraesentaneus, showed marked growth promotion activity in lettuce seedlings. Antonio M. Echavarren of the Institute of Chemical Research of Catalonia (ICIQ) assembled all three rings of 34 in a single step, cyclizing 32 to 33 (Org. Lett. 2018, 20, 5784. DOI: 10.1021/acs.orglett.8b02478).