Enantioselective Preparation of Alkylated Centers: The Bisai Synthesis of (-)-Physovenine
Shengkun Li of Nanjing Agricultural University and Xumu Zhang of Rutgers achieved (Org. Lett. 2015, 17, 3782. DOI: 10.1021/acs.orglett.5b01758) high selectivity in the preparation of 2 by the enantioselective hydrogenation of 1. Guohua Hou of Beijing Normal University established (J. Am. Chem. Soc. 2015, 137, 10177. DOI: 10.1021/jacs.5b06418) that either geometric isomer of 3 could be reduced to 4 in high ee. Professor Hou also found (Adv. Synth. Catal. 2015, 357, 3875. DOI: 10.1002/adsc.201500723) that the acid 6 could be prepared in high ee by hydrogenation of 5 followed by oxidation.
Simon Jones of the University of Sheffield showed (J. Org. Chem. 2015, 80, 11468. DOI: 10.1021/acs.joc.5b02177) that the glutarimide 7 could be desymmetrized by oxazoborolidine-catalyzed reduction. Further reduction delivered the lactam 8.
Sarah E. Reisman of Caltech developed (J. Am. Chem. Soc. 2015, 137, 10480. DOI: 10.1021/jacs.5b06466) conditions for the assembly of 11 by the enantioselective coupling of 10 with the racemic chloronitrile 9. Kun Wei and Yu-Rong Yang of the Kunming Institute of Biology effected (Chem. Commun. 2015, 51, 17471. DOI: 10.1039/C5CC07221B) the coupling of 12 with 13 to give the branched product 14 in high ee. John F. Hartwig of the University of California, Berkeley reported (J. Am. Chem. Soc. 2015, 137, 13972. DOI: 10.1021/jacs.5b09980) parallel results. Hyeung-geun Park of Seoul National University used (Adv. Synth. Catal. 2015, 357, 2841. DOI: 10.1002/adsc.201500560) a quaternary ammonium salt to catalyze the enantioselective coupling of 15 with 16 to give 17. Andreas Pfaltz of the University of Basel and Carlos Roque Duarte Correia of the State University of Campinas coupled (Angew. Chem. Int. Ed. 2015, 54, 14036. DOI: 10.1002/anie.201507927) the diazonium salt 18 with the diol 19 to give, after oxidation, the lactone 20.
Amir H. Hoveyda of Boston College devised (J. Am. Chem. Soc. 2015, 137, 8948. DOI: 10.1021/jacs.5b05805) the reagent 22, that could be coupled with 21 to give 23 in high ee. Eric Meggers of the Philipps-Universitšt Marburg irraditated (J. Am. Chem. Soc. 2015, 137, 9551. DOI: 10.1021/jacs.5b06010) 24 with visible light in the presence of bromotrichloromethane and an Ir catalyst to give 25. Wenhui Hu and Junling Zhao of the Guangzhou Insitutes of Biomedicine and Health took (Adv. Synth. Catal. 2015, 357, 2437. DOI: 10.1002/adsc.201500079) a different approach to the nitro ester 26, adding malononitrile 27 to give 28.
Quaternary α-formyl esters such as 31 are quite fragile. Nevertheless, Tomonori Misaki and Takashi Sugimura of the University of Hyogo were able (Chem. Eur. J. 2015, 21, 18971. DOI: 10.1002/chem.201504479) to effect conjugate addition of 29 to 30 to give 31.
There are a variety of indole-derived alkaloids such as (-)-Physovenine (34) with quaternary alkylated benzylic centers. Alakesh Bisai of the Indian Institute of Science Education and Research Bhopal established (Org. Lett. 2015, 17, 5922. DOI: 10.1021/acs.orglett.5b03082) a general approach to such alkaloids, the enantioselective condensation of 32 with formaldehyde to give 33.