Organic Chemistry Portal
Organic Chemistry Highlights

Monday, March 18, 2024
Douglass F. Taber
University of Delaware

Functional Group Protection: The White Synthesis of Usaramine

Zhaohua Yan of Nanchng University used Ph3P·I2 to cleave both the phenyl ether and the alkyl ether of 1, leading to the iodide 2 (Tetrahedron Lett. 2023, 121, 154460. DOI: 10.1016/j.tetlet.2023.154460). In this way, a phenyl ether can be a protected form of the corresponding alkyl iodide. Supriyo Majumder of Bharat Petroleum Corporation prepared the acetate 5 by using the diketone 4 to acylate the alcohol 3 (Org. Biomol. Chem. 2023, 21, 3837. DOI: 10.1039/D3OB00116D).

Jian-Ping Qu of Nanjing Tech University and Yan-Biao Kang of the University of Science and Technology of China devised visible light conditions for converting the sulfonamide 6 to the amine 7 (Org. Lett. 2023, 25, 816. DOI: 10.1021/acs.orglett.2c04346). Victoria Alcázar of the Polytechnic University of Madrid and Joaquín R. Morán of the University of Salamanca showed that reduction liberated the free amine 9 from the amide 8 (Org. Lett. 2023, 25, 4103. DOI: 10.1021/acs.orglett.3c01334). Hamed L. Ali of Texas A&M and Samy Mohamady of the British University in Egypt developed the reagent 11 for converting an amine 10 to the phthalimide 12 (Eur. J. Org. Chem. 2023, 26, e202300207. DOI: 10.1002/ejoc.202300207). Yinjun Xie of the Ningbo Institute of Materials Technology and Engineering removed the phthalimide protecting group from 12 by hydrogenation with a silver catalyst, isolating the liberated amine as the hydrochloride 13 (Org. Lett. 2023, 25, 3066. DOI: 10.1021/acs.orglett.3c00887).

Hans-Achim Wagenknecht of the Karlsruhe Institute of Technology used visible light and a photocatalyst to protect the aldehyde 14 as its acetal 15 (Chem. Eur. J. 2023, 29, e202203767. DOI: 10.1002/chem.202203767). Meng Deng and Nan Li of Luoyang Normal University effected oxidative cleavage of the tertiary allylic alcohol 16 to the ketone 17 (Org. Lett. 2023, 25, 2420. DOI: 10.1021/acs.orglett.3c00556).

TomᚠSlanina of the Institute of Organic Chemistry and Biochemistry of the Czech Academy of Sciences hydrolyzed the t-butyl ester of 18 to give 19, leaving the ethyl ester intact (J. Org. Chem. 2023, 88, 6932. DOI: 10.1021/acs.joc.3c00238). Yan Zhao of Iowa State University devised a difunctional synthetic esterase that hydrolyzed the aryl ester 20 to the phenol 21 and the acid 22 at neutral pH (J. Org. Chem. 2023, 88, 3282. DOI: 10.1021/acs.joc.2c02570). Yasuhiro Nishikawa and Osamu Hara of Meijo University showed that the amide 23 could be converted to the carboxylic acid 24 with a Ni catalyst (Org. Lett. 2023, 25, 895. DOI: 10.1021/acs.orglett.2c03670). Wenbo H. Liu of Sun Yat-sen University demonstrated that the reagent 26 could selectively arylate even very hindered amides such as 25, to give an intermediate that could be cleaved to the carboxylic acid 27 under irradiation (Org. Lett. 2023, 25, 2948. DOI: 10.1021/acs.orglett.3c00354).

The pyrrolizidine alkaloids, represented by usaramine 30, isolated from the West Indian rattlebox Crotalaria usaramoensis, show powerful hepatotoxic and carcinogenic properties. Attempts to elaborate the macrolactone onto the protected retronecine 28 led instead to aromatization to the pyrrole. The late James D. White of Oregon State University showed that it was possible to protect the amine of 28 as the borane complex 29, and carry that through several steps of the synthesis before liberating the amine by warming with ethanol (J. Org. Chem. 1989, 54, 4268. DOI: 10.1021/jo00279a005).

D. F. Taber, Org. Chem. Highlights 2024, March 18.