C-N Ring Construction: The Topczewski Synthesis of Hasubanan
Jian Wang of Tsinghua University added the azirine 2 to the aldehyde 1 to give the aziridine 3 in high ee (Angew. Chem. Int. Ed. 2018, 57, 3767. DOI: 10.1002/anie.201712785). Matthew J. Gaunt of the University of Cambridge cyclized the amine 4 to the azetidine 5 (Angew. Chem. Int. Ed. 2018, 57, 3178. DOI: 10.1002/anie.201800519).
X. Peter Zhang of Boston College, taking advantage of the facile in situ generation of alkyl diazo intermediates, developed a Co catalyst that cyclized 6 to pyrrolidine 7 in high ee (J. Am. Chem. Soc. 2018, 140, 4792. DOI: 10.1021/jacs.8b01662). Hans-Günther Schmalz of the University of Cologne achieved substantial diastereoselectivity in the addition of 9 to 8. Cu-mediated addition delivered the complementary diastereomer (Eur. J. Org. Chem. 2018, 455. DOI: 10.1002/ejoc.201701584). Tianning Diao of New York University devised the cyclization of 11 and in situ coupling with bromobenzene, leading to 12 (Chem. Commun. 2018, 54, 2558. DOI: 10.1039/C8CC00358K). Ramesh Giri of the University of New Mexico reported a carbonylative version of this cyclization (J. Org. Chem. 2018, 83, 3013. DOI: 10.1021/acs.joc.7b03128) (not illustrated). Fei Xue and Yong Qin of Sichuan University cyclized 13 to 14 (Tetrahedron Lett. 2018, 59, 1999. DOI: 10.1016/j.tetlet.2018.04.019).
Nicolai Cramer of the Ecole Polytechnique Fédérale de Lausanne achieved substantial enantioselectivity in the cyclization of 15 to 16 (J. Am. Chem. Soc. 2018, 140, 4489. DOI: 10.1021/jacs.8b01181). Guosheng Liu of the Shanghai Institute of Organic Chemistry also accomplished high ee in the cyclization of the prochiral 17 to 18 (J. Am. Chem. Soc. 2018, 140, 7415. DOI: 10.1021/jacs.8b03767). Armando Córdova of Stockholm University took advantage of the organocatalysed Michael addition of malonate 20 to 19, converting the product via condensation with 21 to the piperidone 22 (Eur. J. Org. Chem. 2018, 1158. DOI: 10.1002/ejoc.201701789). Dale G. Drueckhammer of Stony Brook University established the cascade addition of 24 to 23, leading through bromination and azide displacement to the piperidine 25 (Tetrahedron Lett. 2018, 59, 1776. DOI: 10.1016/j.tetlet.2018.03.080).
Dimitris Kalaitzakis and Georgios Vassilikogiannakis of the University of Crete used an organocatalyst to mediate the addition of the pyrrolidinone from the oxidative cleavage of 26 to the unsaturated aldehyde 27, leading to 28 (Org. Lett. 2018, 20, 1146. DOI: 10.1021/acs.orglett.8b00076). Chang-Mei Si and Bang-Guo Wei of Fudan University incorporated two equivalents of the aldehyde 30 in the conversion of 29 to 31 (Org. Lett. 2018, 20, 1090. DOI: 10.1021/acs.orglett.7b04056).
Allyic azides readily undergo 1,3-rearrangement. The elegant rearrangement and cyclization of 32 to 33 developed by Joseph J. Topczewski of the University of Minnesota set the stage for the subsequent reductive cyclization to hasubanan 34 (J. Am. Chem. Soc. 2018, 140, 1211. DOI: 10.1021/jacs.7b11299).