C-N Ring Construction: The Soˇs Synthesis of Aspidofractinine
Jiajing Tan of the Beijing University of Chemical Technology and Sheng Zhang and Kun Xu of Nanyang Normal University used catalytic iodide under oxidizing electrolysis conditions to cyclize the carbamate 1 to the aziridine 2 (Org. Lett. 2019, 21, 9430. ). Vincent N. G. Lindsay of North Carolina State University assembled the β-lactam 4 by combining N-hydroxy benzylamine with the readily-prepared cyclopropanone surrogate 3 (Angew. Chem. Int. Ed. 2020, 59, 18655. ).
Now that CÚcile Dehoux of the UniversitÚ Paul Sabatier cyclized the allene 5 to the dihydropyrrole 6 (Org. Biomol. Chem. 2020, 18, 7852. ). Kazuaki Ishihara of Nagoya University prepared the pyrrolidine 9 by combining the enone 7 with the propargyl sulfonamide 8 (Angew. Chem. Int. Ed. 2020, 59, 16470. ). Zhengjie He of Nankai University used a designed phosphine to mediate the construction of 12 by the combination of 10 with 11 (Adv. Synth. Catal. 2020, 362, 2760. ). Daniel Romo of Baylor University showed that a quinine-derived catalyst directed the addition of 14 to 13, leading to 15 (Org. Lett. 2020, 22, 9282. ).
Mary P. Watson of the University of Delaware achieved high ee in the addition of the alkyne 17 to racemic 16, leading to the piperidine 18 (ACS Catal. 2020, 10, 13820. ). Xiao-Chen Wang, also of Nankai University, devised an enantiomerically-pure bis borane that catalyzed the reduction of the pyridine 19 to the piperidine 20 (Angew. Chem. Int. Ed. 2020, 59, 18452. ). Pinhong Chen and Guosheng Liu of the Shanghai Institute of Organic Chemistry used 22 to effect the oxidative cyclization of 21 to 23 (Angew. Chem. Int. Ed. 2020, 59, 17239. ). Masato Iwatsuki of Kitasato University and Hiroki Oguri of the University of Tokyo cyclized 24 to 25 (J. Org. Chem. 2020, 85, 9694. ).
Arjan W. Kleij of ICIQ coupled the vinyl lactone 26 with aniline, then cyclized that product to the caprolactam 27 (Chem. Sci. 2020, 11, 8839. ). Alkenes such as 27 are readily converted into cyclic quaternary centers in high ee (J. Am. Chem. Soc. 2004, 126, 13900. ). Sanghee Kim of Seoul National University assembled the indolizidine 30, maintaining the absolute configuration of the proline derivative 28 in the course of the combination with the ynone 29 (Adv. Synth. Catal. 2020, 362, 2941. ).
Aspidofractinine 34, isolated from the African shrub Pleiocarpa pycnantha, is one of a family of alkaloids with cardiovascular activity. Tibor Soˇs of the Research Center for Natural Sciences assembled 31 in 91% ee by an organocatalyzed Robinson annulation, then combined the cyclohexenone with aziridine 32 to give the tricyclic 33 (Angew. Chem. Int. Ed. 2020, 59, 13547. ).