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Visible-light Promoted Bromination of Phenols and Synthesis of Dihydrobenzofurans

Author: LiZhe
Tutor: XiaWuJiong
School: Harbin Institute of Technology
Course: Physical and chemical
Keywords: Visible-light Phenols Bromination Dihydrobenzofurans
CLC: O621.3
Type: Master's thesis
Year: 2013
Downloads: 21
Quote: 0
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Abstract


Visible-promoted reaction has many advantages which the traditional chemicalreactions don’t have. Due to the general organic molecules don’t have the ability ofabsorbing the visible light, so the reserach of photochemical reactions wererestricted to UV-light. In recent years, the visible light promoted reaction has beenrapidly developed after the discovery of photocatalyst. For example, the reductivedehalogenation, reductive epoxide and aziriding opening,-arylation of amides,arene and heteroarene trifluoromethylation, the cleavage of C-C bond, etc. Based onthis synthetic strategy, we investigate the visible-light promoted the bromination ofphenols and synthesis dihydrobenzofurans via aryl C-H activation.Bromophenols sever as important synthetic intermediates for various naturallyoccurring biologically active compounds and are also the important contituents ofindustry chemicals. Bromination of the phenols under visible-light induced wasdetected for the first time. About the bromination of phenols,(4-methoxyphenoxy)trimethylsilane as the representative substrate was tried to undergo the reactionunder the visible-light and optimize the reaction conditions. We further examinedthe reaction by replacement of CBr4with Na2S2O8as oxidative quencher, which alsoformed the product.With the two optimized conditions in hand, we prepared16phenols which were subjected to the photocatalytic reaction. To our surprise anddelight, all achieved high yield and good selectivity. Due to the research results, weconjecture the reaction undergo a oxidative quenching cycle. And in the processphenols lost an electron to form a radical cations which were attacked by thebromine anion. As a result, the bromophenols formed.Dihydrobenzofuran derivatives are unique structural skeletons in manybiologically active molecules and natural products. They are present in moleculesacting as potent inducers of the anticarcinogentic marker enzyme, antifungal, etc.This article tells us (4-methoxy-phenoxy)trimethylsilane reacting with styrenesunder visible-light could get dihydrobenzofuran derivatives. About the synthesis ofdihydrobenzofurans, a series of visible-light conditions were used in the reaction of(4-methoxy-phenoxy)trimethylsilane with styrene. The scope of this protocol wastested by subjection of (4-methoxy-phenoxy)trimethylsilane with different styrenesunder the same reaction conditions.Notably, the naturally occurring product whichalso has anti-flammatory effect, Corsifuran A, could be synthesized in one step in42%yield in this protocol.

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CLC: > Mathematical sciences and chemical > Chemistry > Organic Chemistry > Organic Chemistry general issues > Synthetic organic chemistry
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