620-20-2Relevant articles and documents
N -Hydroxyphthalimide/benzoquinone-catalyzed chlorination of hydrocarbon C-H bond using N -chlorosuccinimide
Li, Zi-Hao,Fiser, Béla,Jiang, Biao-Lin,Li, Jian-Wei,Xu, Bao-Hua,Zhang, Suo-Jiang
supporting information, p. 3403 - 3408 (2019/04/01)
The direct chlorination of C-H bonds has received considerable attention in recent years. In this work, a metal-free protocol for hydrocarbon C-H bond chlorination with commercially available N-chlorosuccinimide (NCS) catalyzed by N-hydroxyphthalimide (NHPI) with 2,3-dicyano-5,6-dichlorobenzoquinone (DDQ) functioning as an external radical initiator is presented. Aliphatic and benzylic substituents and also heteroaromatic ones were found to be well tolerated. Both the experiments and theoretical analysis indicate that the reaction goes through a process wherein NHPI functions as a catalyst rather than as an initiator. On the other hand, the hydrogen abstraction of the C-H bond conducted by a PINO species rather than the highly reactive N-centered radicals rationalizes the high chemoselectivity of the monochlorination obtained by this protocol as the latter is reactive towards the C(sp3)-H bonds of the monochlorides. The present results could hold promise for further development of a nitroxy-radical system for the highly selective functionalization of the aliphatic and benzylic hydrocarbon C-H.
Mild Aliphatic and Benzylic Hydrocarbon C-H Bond Chlorination Using Trichloroisocyanuric Acid
Combe, Sascha H.,Hosseini, Abolfazl,Parra, Alejandro,Schreiner, Peter R.
, p. 2407 - 2413 (2017/03/11)
We present the controlled monochlorination of aliphatic and benzylic hydrocarbons with only 1 equiv of substrate at 25-30 °C using N-hydroxyphthalimide (NHPI) as radical initiator and commercially available trichloroisocyanuric acid (TCCA) as the chlorine source. Catalytic amounts of CBr4 reduced the reaction times considerably due to the formation of chain-carrying ·CBr3 radicals. Benzylic C-H chlorination affords moderate to good yields for arenes carrying electron-withdrawing (50-85%) or weakly electron-donating groups (31-73%); cyclic aliphatic substrates provide low yields (24-38%). The products could be synthesized on a gram scale followed by simple purification via distillation. We report the first direct side-chain chlorination of 3-methylbenzoate affording methyl 3-(chloromethyl)benzoate, which is an important building block for the synthesis of vasodilator taprostene.
A duality of mechanisms for the fragmentation of substituted benzyloxychlorocarbenes
Moss, Robert A.,Ma, Yan,Sauers, Ronald R.
, p. 13968 - 13969 (2007/10/03)
Substituted benzyloxychlorocarbenes (X-PhCH2OCCl) were generated photochemically at 25 °C in dichloroethane from appropriate diazirine precursors. Fragmentations of the carbenes produced were determined by laser flash photolysis. The data (X, kfrag in s-1) were: p-Me, 2.6 × 105; p-Ph, 8.3 × 104; H, 6.0 × 104; p-Cl, 5.2 × 104; m-Cl, 1.3 × 105; p-F3C, 2.1 × 106; p-O2N, 6.3 × 106. A Hammett correlation of log kfrag versus σ+ was parabolic. The curvature was taken to imply the gradual change of the fragmentation mechanism from predominantly heterolytic for X-PhCH2CCl with electron-donating X (with developing positive charge on the benzylic carbon in the transition state) to predominantly homolytic for carbenes with electron-withdrawing X. This idea was supported by computational studies. Copyright
