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Monday, July 16, 2018
Douglass F. Taber
University of Delaware

Alkylated Stereogenic Centers: The Cao Synthesis of Chanoclavine I

Vy M. Dong of the University of California, Irvine used 2 in conjunction with a Rh catalyst to selectively reduce the allene 1 to 3 (Nature Commun. 2017, 8, 784. ). Jaesook Yun of Sungkyunkwan University effected enantioselective hydroboration of 4, leading to 5 (J. Am. Chem. Soc. 2017, 139, 13660. ). Jianwei Sun of the Hong Kong University of Science and Technology achieved high ee in the reduction of 6 to 8, mediated by 7 (Angew. Chem. Int. Ed. 2017, 56, 11966. ). Marko D. Mihovilovic of TU Wien, Marco W. Fraaije of the University of Groningen and Manfred T. Reetz of the Max-Planck-Institut für Kohlenforschung converted an enzyme that oxidized 9 to the S lactone to a mutant that oxdidized 9 to the R lactone 10 (Org. Biomol. Chem. 2017, 15, 9824. ).

Syuzzana R. Harutyunyan, also of the University of Groningen, devised conditions for the enantioselective conjugate addition of an alkyl Grignard reagent to the amide 11, leading to 12 (J. Am. Chem. Soc. 2017, 139, 14224. ). Related conjugate additions were described by Stephen P. Fletcher of the University of Oxford (Chem. Commun. 2017, 53, 10216. ) and by Andrew D. Smith of the University of St Andrews (Angew. Chem. Int. Ed. 2017, 56, 12282. ). David W. C. MacMillan of Princeton University effected direct addition of the aldehyde 13 to the styrene 14 to give 15 (Nature Chem. 2017, 9, 1073. ). Wen-Jing Xiao of Central China Normal University assembled 18 by coupling the linchpin 17 with 16, followed by the addition of formaldehyde (J. Am. Chem. Soc. 2017, 139, 12847. ). Long-Wu Ye of Xiamen University added 20 to 19 to give an intermediate that was then rearranged to 21 (J. Org. Chem. 2017, 82, 10149. ).

Masanori Yoshida of the National Institute of Technology directly established the quaternary center of 24 by alkylating 22 with allyl alcohol 23 (J. Org. Chem. 2017, 82, 12821. ). Sanzhong Luo of the Institute of Chemistry of the Chinese Academy of Sciences alkynylated 22 with 25, leading to 26 (Org. Lett. 2017, 19, 4924. ). Brian M. Stoltz of Caltech and Ilan Marek of Technion rearranged 27 to 28 in high ee (J. Am. Chem. Soc. 2017, 139, 9615. ). Yong-Qiang Wang of Northwest University coupled 29 with 30 to give 31 (Org. Lett. 2017, 19, 3516. ).

Chanoclavine I (35), isolated from the ergot fungus Claviceps purpurea, is the biosynthetic precursor of nearly all of the ergot alkaloids. In the course of a synthesis of 35, Xiao-Ping Cao of Lanzhou University opened the inexpensive styrene oxide 32 with the Grignard reagent 33, leading to 34 (J. Org. Chem. 2017, 82, 7774. ).

D. F. Taber, Org. Chem. Highlights 2018, July 16.
URL: https://www.organic-chemistry.org/Highlights/2018/16July.shtm