Selective functionalization of benzylic C-H bonds of two different benzylic ethers by bowl-shaped N-hydroxyimide derivatives as efficient organoradical catalysts

A highly efficient, site-selective benzylic C-H bond amination of two different benzylic ether substrates was described by using bowl-shaped N-hydroxyimide organoradical catalysts with diethyl azodicarboxylate. The synthetic utility of this...

Nickel-Catalyzed Cross-Electrophile Coupling of the Difluoromethyl Group for Fluorinated Cyclopropane Synthesis

Herein, we report a new strategy for fluorinated cyclopropane synthesis. Photocatalytic olefin difluoromethylation is coupled with a nickel-catalyzed intramolecular cross-electrophile coupling (XEC) reaction between a difluoromethyl moiety and a benzylic ether. To the best of our knowledge, this is the first example of a XEC reaction employing a difluoromethyl group as an electrophile. A plausible mechanism is highlighted, and DFT calculations are included to support the observed stereochemical outcome.

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•5H₂O 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.