Organocatalyzed C-C Ring Construction: The Takakawa Synthesis of Salinipostin A
Peng-Fei Xu of Lanzhou University used a Cinchona alkaloid-derived catalyst to direct the addition of 1 to 2. Chlorination with NCS followed by cyclization completed the assembly of 3 (J. Org. Chem. 2019, 84, 10292. DOI: 10.1021/acs.joc.9b01454). Ryan Gilmour of Westfälische Wilhelms-Universität Münster mediated the cyclization of 4 to 5 with a thioxanthone photocatalyst (Org. Lett. 2019, 21, 9724. DOI: 10.1021/acs.orglett.9b03882).
Tõnis Kanger of the Tallinn University of Technology showed that a Cinchona alkaloid-derived catalyst effectively directed the rearrangement of 6 to 7 (Org. Lett. 2019, 21, 4976. DOI: 10.1021/acs.orglett.9b01495). Building on the work of You (Org. Lett. 2014, 16, 1810. DOI: 10.1021/ol5005565), Masahiro Terada of Tohoku University used a BINOL-derived phosphoramide to rearrange 8 to the cyclopentanone 9 (ACS Catal. 2019, 9, 6846. DOI: 10.1021/acscatal.9b01780). Zhi-Men Chen of Shangahi Jiao Tong University, Yong-Qiang Tu, also of Lanzhou University, and Xiaoguang Bao of Soochow University described a related investigation (Angew. Chem. Int. Ed. 2019, 58, 12491. DOI: 10.1002/anie.201907115). Tohru Yamada of Keio University achieved clean chirality transfer in the conversion of 10 to the cyclopentenone 11 (Org. Lett. 2019, 21, 6628. DOI: 10.1021/acs.orglett.9b02107). Han Liu of Aarhus University, Qingshan Li and Shurong Ban of Shanxi Medical University and Heng Song of Wuhan University also used a Cinchona alkaloid-derived catalyst to mediate the addition of 13 to 12, leading to 14 (J. Org. Chem. 2019, 84, 15655. DOI: 10.1021/acs.joc.9b02176).
Professor Terada used a phosphoric acid based on a BINOL dimer to direct the assembly of 17 by the Diels-Alder reaction of 15 with 16 (Chem. Lett. 2019, 48, 260. DOI: 10.1246/cl.180977). Kazuaki Ishihara of Nagoya University employed a quaternary ammonium salt to mediate the oxidation of 18 with Oxone to the spirolactone 19 (ACS Catal. 2019, 9, 11619. DOI: 10.1021/acscatal.9b04322). Mikel Oiarbide and Claudio Palomo of the Universidad de Pais Vasco showed that a Cinchona alkaloid-derived catalyst was basic enough to promote the preparation of 22 by the addition of 20 to 21 (Chem. Eur. J. 2019, 25, 9701. DOI: 10.1002/chem.201901694). E. J. Corey of Harvard University used tetramethyguanidine to effect elimination of HBr from 23, and then in situ a Cinchona alkaloid-derived catalyst to guide the addition of nitromethane 24 to the resulting nitroso intermediate, leading to 25 (J. Am. Chem. Soc. 2019, 141, 20058. DOI: 10.1021/jacs.9b12315).
David W. Lupton of Monash University observed substantial diastereoselectivty in the N-heterocyclic carbene-catalyzed cyclization of 26 to 27 (Angew. Chem. Int. Ed. 2019, 58, 11483. DOI: 10.1002/anie.201905475). Samuel H. Gellman of the University of Wisconsin designed a foldamer that catalyzed the conversion of 28 to 29 (Science 2019, 366, 1528. DOI: 10.1126/science.aax7344).
Salinipostin A (32), isolated from a Salinispora species found in marine sediment, shows potent anti-malarial activity. Hirosato Takikawa of the University of Tokyo set the absolute configuration of 32 by the addition of 30 to 16 to give 31 (Tetrahedron Lett. 2019, 60, 150917. DOI: 10.1016/j.tetlet.2019.07.008).