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Monday, March 16, 2015
Douglass F. Taber
University of Delaware

Oxidation of Organic Functional Groups

Cancheng Guo of Hunan University devised (J. Org. Chem. 2014, 79, 2709. ) conditions for the oxidative cleavage of an alkyne 1 to the esters 2 and 3. Hirokazu Arimoto of Tohoku University found (Chem. Commun. 2014, 50, 2758. ) that IBX oxidized a primary alcohol 4 to the acid 5 one carbon shorter. David Milstein of the Weizmann Institute of Science uncovered (J. Am. Chem. Soc. 2014, 136, 2998. ) conditions for the direct oxidation of the cyclic amine 6 to the lactam 7, with concomitant evolution of H2.

Cyclic ene sulfonamides such as 9 are versatile synthetic intermediates. Henri Doucet of the Université de Rennes reported (Adv. Synth. Catal. 2014, 356, 119. ) the regioselective conversion of 8 to 9. In this case, the oxidizing agent was the organo-PdBr intermediate.

There have been many reports of the functionalization of the oxygenated carbons of cyclic ethers, as exemplified by the conversion of 10 to 11, observed (J. Org. Chem. 2014, 79, 3847. ) by Jianlin Han of Nanjing University. If these methods were regioselective with an acyclic benzyl ether, this could be a new method for the removal of that common protecting group. Jianliang Xiao of the University of Liverpool described (J. Am. Chem. Soc. 2014, 136, 8350. ) a selective benzylic ether oxidation that converted 12 to 13.

Baris Temelli of Hacettepe University effected (Synthesis 2014, 46, 1407. ) the conversion of a primary nitro compound 14 into the corresponding nitrile 15. Jean-Michel Vatèle of Université Lyon 1 oxidized (Synlett 2014, 25, 1275. ) the primary alcohol 16 to the nitrile 17.

Many methods have been put forward for the oxidation of primary alcohols to aldehydes and secondary alcohols to ketones. Piperidinium oxy radicals such as TEMPO are widely used to catalyze this transformation. Yoshikazu Kimura of Iharanikkei Chemical Industry Co. Ltd. established (Synlett 2014, 25, 596. ) a manufacturing process for crystalline NaOCl•5H20 that served as the bulk oxidant for the conversion of 18 to 19. Neither a ketone nor an aldehyde was chlorinated under the reaction conditions. Yoshiharu Iwabuchi of Tohoku University showed (Angew. Chem. Int. Ed. 2014, 53, 3236. ) that with his piperidinium oxy radical AZADO and Cu catalysis, air could be the bulk oxidant for the otherwise difficult conversion of the amino alcohol 20 to the amino ketone 21. Using solvent acetone as the hydride acceptor and a highly active Ru catalyst, Zhengkun Yu of the Dalian Institute of Chemical Physics converted (Tetrahedron Lett. 2014, 55, 1585. ) the alcohol 18 to the alcohol 19 in just 30 minutes. Jian Chen of Central China Normal University described (Tetrahedron Lett. 2014, 55, 1736. ) the oxidation of the alkene 22 to the α-aryl ketone 23.

Tun-Cheng Chien of the National Taiwan Normal University added (Org. Lett. 2014, 16, 892. ) hydroxylamine to the nitrile 24 to generate the amidoxime (not illustrated). Further addition of TsCl led to rearrangement to the cyanamide 25. Bhubaneswar Mandal of the Indian Institute of Technology Guwahati used (J. Org. Chem. 2014, 79, 3765. ) ethyl 2-cyano-2-(4-nitrophenylsulfonyloxyimino)acetate (4-NBsOXY) to convert the acid 26 into the N-hydroxyamide (not illustrated). Further exposure to the activating agent led to rearrangement to the isocyanate (not illustrated), that was coupled with the amine 27 to give the urea 28.

D. F. Taber, Org. Chem. Highlights 2015, March 16.