Arrays of Stereogenic Centers: The Ishikawa Synthesis of Secologanin
Scott E. Denmark of the University of Illinois devised a selenium catalyst that directed the addition of 2 to 1, leading to 3 (J. Am. Chem. Soc. 2019, 141, 19161. ). Wen-Hua Zheng of Nanjing University found that a chiral phosphoric acid was effective for the oxidative discrimination of the two enantiomers of 4, leading to 5 and 6 (Org. Lett. 2019, 21, 5197. ).
Yoshiji Takemoto of Kyoto University showed that a diamine catalyzed the enantioselective Mannich addition of the isonitrile 8 to the imine 7, to give 9 (ACS Catal. 2019, 9, 10087. ). Markus Kalesse of the Gottfried Leibniz Universitšt Hannover used a valine-derived borane to assemble 12 by the addition of the ketene silyl acetal 11 to 10 (Chem. Eur. J. 2019, 25, 10080. ). Yujiro Hayashi of Tohoku University followed the diarylprolinol-catalyzed addition of 13 to 14 with a Wittig reaction, leading to 15 (Chem. Asian J. 2019, 14, 4146. ). Jeffrey S. Johnson of the University of North Carolina used a Rh catalyst to equilibrate the double bond of 16 into conjugation with the carbonyl, then to effect conjugate addition selectively to one of the two resulting enantiomers, leading to full conversion to 17 (ACS Catal. 2019, 9, 11614. ).
Barry M. Trost of Stanford University established the alkylated quaternary center of 20 by the Mannich condensation of 19 with 18 (J. Am. Chem. Soc. 2019, 141, 16085. ). Mei-Xin Zhao of the East China University of Science and Technology used a Cinchona-derived catalyst to add 21 to 22, leading to 23 (Org. Chem. Front. 2019, 6, 3879. ).
Yasuhio Yamashita and Shū Kobayashi of the University of Tokyo found that a crown ether effectively directed the assembly of 26 by the addition of 25 to 24 (Adv. Synth. Catal. 2019, 361, 3807. ). Xiaohua Liu and Xiaoming Feng of Sichuan University used a Sc catalyst to mediate the enantioselective Baeyer-Villiger oxidation of the prochiral ketone 27 to the lactone 28 (Chem. Sci. 2019, 10, 7003. ). Chuan-Jin Hou of the Dalian Polytechnic University and Xiang-Ping Hu of the Dalian Institute of Chemical Physics showed that a diamine catalyst could organize the addition of diethyl zinc to 29, followed by the addition of the resulting enolate to 30, leading to 31 (Tetrahedron 2019, 75, 3943. ). Pu-Sheng Wang and Liu-Zhu Gong of the University of Science and Technology of China devised the oxidative coupling of 33 with 32 to give 34 (Angew. Chem. Int. Ed. 2019, 58, 16806. ).
Secologanin 38 plays a central role in the assembly of monoterpenoid indole alkaloids, both biosynthetically and chemically. Hayato Ishikawa of Kumamoto University devised a route to 38, based on the Hayashi catalyst-mediated addition of 36 to 35 to give 37 (Chem. Eur. J. 2019, 25, 8996. ).