2020年1月8日

A metal‐free deoxygenation and reductive disilylation of nitroarenes was achieved using N,N′‐bis(trimethylsilyl)‐4,4′‐bipyridinylidene (1) under mild and neutral reaction conditions, and a broad functional group tolerance was possible in this reaction. Mono‐deoxygenation, giving a synthetically valuable N,O‐bis(trimethylsilyl)phenylhydroxylamine (7 a) as a readily available and safe phenylnitrene source from nitrobenzene, and double‐deoxygenation, giving N,N‐bis(trimethylsilyl)anilines 8, were easily controlled by varying the amounts of 1 and reaction temperature as well as adding dibenzothiophene (DBTP). Reaction of 2‐arylnitrobenzenes with 1 resulted in the formation of the corresponding carbazoles 14 via in situ‐generated phenylnitrene species derived by thermolysis of N,O‐bis(trimethylsilyl)phenylhydroxylamines 7, followed by their subsequent intramolecular C−H insertion. In addition, the intramolecular N−N coupling reaction proceeded in the reduction of 2,2′‐dinitrobiphenyl derivatives by 1, giving the corresponding benzo[c]cinnolines.

A metal-free deoxygenation of sulfoxides to sulfides was also established under mild conditions using a stoichiometric amount of 1,1′-bis(trimethylsilyl)-1H,1′H-4,4′-bipyridinylidene (1) as a reducing reagent which generated 4,4′-bipyridine and hexamethyldisiloxane as less toxic organic waste. This synthetic protocol was applicable to a wide variety of functionalized diaryl, alkyl aryl, and dialkyl sulfoxides with high functional group compatibility: sulfoxides bearing O- or N-protecting groups, such as O-Ac, O-TBS, N-Cbz, N-Ts, resulted in highly chemo-selective reduction of only the sulfoxide portion.

1. Bhattacharjee, A.; Hosoya, H.; Ikeda, H.; Nishi, K.; Tsurugi, H.; Mashima, K. Metal-Free Deoxygenation and Reductive Disilylation of Nitroarenes by Organosilicon Reducing Reagents. Chem. - Eur. J. 2018, 24, 11278−11282.
2. Bhattacharjee, A.; Hosoya,; Yurino, T.; Tsurugi, H.; Mashima, K. Metal-free Reductive Deoxygenation of Sulfoxides by an Organosilicon Reductant, 1,1′-Bis(trimethylsilyl)-1H,1′H-4,4′-bipyridinylidene. Chem. Lett. 2019 , 48, 888 – 890.