Alkyl Halides via Visible Light Mediated Dehalogenation

Abstract

Net selective bromination and chlorination of activated C−H bonds can be effected in generally high yield via a simple perhalogenation/dehalogenation sequence. The photochemical reductions require no photocatalyst, relying instead on the formation of an electron donor−acceptor complex of the substrate and reductant, or alternatively autophotocatalysis. Some reactions proceed despite any apparent photon absorption, serving as a cautionary tale for other photochemical reactions involving amines. Mechanistic experiments provide an explanation for this observation.

Visible‐light‐mediated Synthesis of Bromo‐containing Azaspirotrienediones from N‐phenylpropynamides

“…Intermediate X loses one molecule of water to give the desired product 3 a . In the process of electron transfer with IX , II loses an electron and is converted to cation III [16] . Cation III is nucleophilically attacked by H 2 O to form intermediate IV , which removes one molecule of HBr to generate a stable molecule V [17] .…”

“…In the process of electron transfer with IX, II loses an electron and is converted to cation III. [16] Cation III is nucleophilically attacked by H 2 O to form intermediate IV, which removes one molecule of HBr to generate a stable molecule V. [17] (b) Under visible-light irradiation, RB is excited to RB*, which excites ground state oxygen (triplet oxygen 3 O 2 ) into excited state oxygen (singlet oxygen 1 O 2 ) through energy transfer. 1 O 2 obtains an electron from VIII and is reduced to superoxide anion (O 2 .À ), which is captured by a proton to produce •OOH, and then •OOH couples with VIII to form X. X loses one molecule of H 2 O to produce 3 a.…”

Progress in Photoinduced Radical Reactions using Electron Donor‐Acceptor Complexes

“…[115] Rathnayake et al developed a visible light induced dehalogenation for selective bromination of activated CÀ H bonds in high yields (Scheme 32). [116] The photochemical reductions proceed without the addition of any photocatalysts and metals, affording a series of monohalogenated ketones, esters, and sulfones products in excellent yields. The generated EDA complex 163 between the substrate 162 and reductant (N,Ndiisopropylethylamine) DIPEA plays an important role to promote the photochemical reaction, which was supported by the UV/vis spectra, 1 H NMR, and 19 F NMR.…”

Selective Debromination of α,α,α‐Tribromomethylketones with HBr–H2O Reductive Catalytic System

“…(Scheme 1 d ). [ 10 ] Herein, we report a selective debromination reaction of α,α,α‐tribromomethylketones in water with Brønsted acid as a catalyst. In this reaction, α‐mono‐ or α,α‐dibromomethylketones can be synthesized selectively in one step by adjusting the amount of HBr and reaction temperature.…”