C-N Ring Construction: Septicine (Kleij) and Gelsemolenine A (Takayama)
Hiroto Kaku and Tetsuto Tsunoda of the Tokushima Bunri University cyclized the diol 1 to the azetidine 2 (Heterocycles 2019, 98, 1525. DOI: 10.3987/COM-19-14171). Michael P. Doyle of the University of Texas at San Antonio converted 3 to 4 with high relative and absolute stereocontrol (Angew. Chem. Int. Ed. 2019, 58, 16188, DOI: 10.1002/anie.201909929; Nature Commun. 2019, 10, 5328, DOI: 10.1038/s41467-019-13326-8).
Long-Wu Ye of Xiamen University showed that 5 could be converted to the pyrrolidine 6 with high diastereocontrol (Chem. Commun. 2019, 55, 9923. DOI: 10.1039/C9CC05295J). Bernhard Breit of the Albert-Ludwigs-Universität Freiburg developed a Rh catalyst for the cyclization of 7 to 8 (Angew. Chem. Int. Ed. 2019, 58, 9994. DOI: 10.1002/anie.201904833). Dongxu Yang and Rui Wang of Lanzhou University assembled 11 by combining 9 with 10 (Adv. Synth. Catal. 2019, 361, 3744. DOI: 10.1002/adsc.201900481). Sanghee Kim of Seoul National University observed high retention of chirality in the cyclization of 12 to 13 (J. Org. Chem. 2019, 84, 14436. DOI: 10.1021/acs.joc.9b01800).
Xinhao Zhang of Peking University Shenzhen Graduate School and Liu-Zhu Gong of the University of Science and Technology of China prepared the piperidine 16 by the arylation of 14 with 15 (Angew. Chem. Int. Ed. 2019, 58, 1803. DOI: 10.1002/anie.201812426). Takuya Kurahashi and Seijiro Matsubara of Kyoto University achieved high regio- and enantiocontrol in the addition of 17 to 18, leading to 19 (Chem. Eur. J. 2019, 25, 8987. DOI: 10.1002/chem.201901563). Fabrice Anizon and Isabelle Abrunhosa-Thomas of the Université Clermont Auvergne cyclized 20 to 21 with high diasterecontrol (Eur. J. Org. Chem. 2019, 7686. DOI: 10.1002/ejoc.201901520). Sébastien Comesse of the Université Le Havre Normandie also achieved high diastereocontrol in the assembly of 24 by the addition of 23 to 22 (Eur. J. Org. Chem. 2019, 7703. DOI: 10.1002/ejoc.201901528).
Kiyosei Takasu, also of Kyoto University, observed high diastereoselectivity in the retro-aldol/alkylation sequence that converted 25 to the trans cylic alkene 26 (Angew. Chem. Int. Ed. 2019, 58, 11836. DOI: 10.1002/anie.201906665). Arjan W. Kleij of ICIQ used SO2F2 to cyclize the diol 27 directly to the alkaloid septicine (28) (Chem. Eur. J. 2019, 25, 15055. DOI: 10.1002/chem.201904223).
The alkaloids of Gelsemium elegans ("heartbreak grass"), as exemplified by gelsemolenine (31), have long fascinated and challenged organic synthesis chemists. Hiromitsu Takayama of Chiba University established a general route to this family of alkaloids, based on the cyclization of 29 to the lactam 30 (Org. Lett. 2019, 21, 7134. DOI: 10.1021/acs.orglett.9b02703).
We note with respect the passing of Rolf Huisgen, one of the founding fathers of our field.