Heteroaromatics: The Scheerer Synthesis of Rupestine M

Azusa Kondoh and Masahiro Terada of Tohoku University constructed the furan 3 by the combination of the alkyne 1 with benzaldehyde 2 (Eur. J. Org. Chem. 2023, 26, e202300425. DOI: 10.1002/ejoc.202300425). Tuanli Yao of the Shaanxi University of Science and Technology, Tao Li of the Chinese Academy of Agricultural Sciences, and Xiangyang Qin of the Air Force Medical University achieved significant diastereoselectivity in the assembly of the furan 6 from the alkyne 4 and butenediol 5 (Org. Lett. 2024, 26, 2018. DOI: 10.1021/acs.orglett.4c00089).

Guang Liang and Jie Li of Hangzhou Medical College and Patrick J. Walsh of the University of Pennsylvania combined the nitrile 7 with the alkyne 8, leading to the pyrrole 9 (Adv. Synth. Catal. 2024, 366, 942. DOI: 10.1002/adsc.202301053). Maya Shankar Singh of Banaras Hindu University oxidize a tertiary amine to the corresponding enamine, then alkylated that in situ with the bromoketone 10, leading to an intermediate that they cyclized to the pyrrole 11 (Chem. Commun. 2024, 60, 5435. DOI: 10.1039/D4CC01043D).

Anil K. Saikia of the Indian Institute of Technology Guwahati effected the halo-aza-Prins cyclization of the bromo alkene 12 with benzaldehyde 2, leading to an intermediate that after double dehydrohalogenation was converted to the pyridine 13 (Org. Biomol. Chem. 2024, 22, 3893. DOI: 10.1039/D4OB00338A).

Bhimapaka China Raju of the Indian Institute of Chemical Technology, Hyderabad prepared the pyridine 16 by combining the imine 14 with two equivalents of ethyl propiolate 15 (Eur. J. Org. Chem. 2024, 27, e202301265. DOI: 10.1002/ejoc.202301265). Graham de Ruiter of Technion-Israel Institute of Technology used a Co catalyst to isomerize the allyl amine 17 to the corresponding enamine, then cyclized that with the enamine 18, leading after dehydrogenation to the pyridine 19 (J. Org. Chem. 2024, 89, 4319. DOI: 10.1021/acs.joc.3c02349). Pablo Barrio and José M. González of the University of Oviedo used a gold catalyst to cyclize the bromoalkyne 20 to the corresponding bromocyclopentene, that after coupling with phenylboronic acid and ozonolysis led to the pyridine 21 (Eur. J. Org. Chem. 2024, 27, e202301274. DOI: 10.1002/ejoc.202301274).

Zheng Li of Northwest Normal University used calcium carbide as a source for acetylene for the cyclization of the diazo intermediate derived from the tosylhydrazone 22 to the indole 23 (Eur. J. Org. Chem. 2024, 27, e202301262. DOI: 10.1002/ejoc.202301262). Ken-ichi Takao and Akihiro Ogura of Keio University used a Ru catalyst to isomerize the allyl ether 24 to the enol ether, that cyclized to the indole 25 (Adv. Synth. Catal. 2024, 366, 465. DOI: 10.1002/adsc.202301304). Xinxin Wu of Soochow University showed that the distal radical derived from the iodo sulfone 26 could be coupled with a diazonium salt, leading to an intermedate that was cyclized to the indole 27 (Org. Lett. 2023, 25, 8814. DOI: 10.1021/acs.orglett.3c03401). Hequan Yao and Aijun Lin of China Pharmaceutical University achieved high ee in the Pd mediated cyclization of 28 to give the indole 29 (ACS Catal. 2024, 14, 8739. DOI: 10.1021/acscatal.4c01325).

Rupestine M (32) was isolated from Artemisia rupestris L., a commonly used Chinese herbal medicine. Jonathan R. Scheerer of the College of William & Mary assembled 32 by the intramolecular hetero Diels-Alder cyclization of the diene derived from 30 to the pyridine 31, followed by reduction (Synthesis 2023, 55, 2319. DOI: 10.1055/s-0042-1751413).