- Thiourea-Mediated Halogenation of Alcohols
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The halogenation of alcohols under mild conditions expedited by the presence of substoichiometric amounts of thiourea additives is presented. The amount of thiourea added dictates the pathway of the reaction, which may diverge from the desired halogenation reaction toward oxidation of the alcohol, in the absence of thiourea, or toward starting material recovery when excess thiourea is used. Both bromination and chlorination were highly efficient for primary, secondary, tertiary, and benzyl alcohols and tolerate a broad range of functional groups. Detailed electron paramagnetic resonance (EPR) studies, isotopic labeling, and other control experiments suggest a radical-based mechanism. The fact that the reaction is carried out at ambient conditions, uses ubiquitous and inexpensive reagents, boasts a wide scope, and can be made highly atom economic, makes this new methodology a very appealing option for this archetypical organic reaction.
- Mohite, Amar R.,Phatake, Ravindra S.,Dubey, Pooja,Agbaria, Mohamed,Shames, Alexander I.,Lemcoff, N. Gabriel,Reany, Ofer
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- Bromination of olefins with HBr and DMSO
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A simple and inexpensive methodology is reported for the conversion of alkenes to 1,2-dibromo alkanes via oxidative bromination using HBr paired with dimethyl sulfoxide, which serves as the oxidant as well as cosolvent. The substrate scope includes 21 olefins brominated in good to excellent yields. Three of six styrene derivatives yielded bromohydrins under the reaction conditions.
- Karki, Megha,Magolan, Jakob
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p. 3701 - 3707
(2015/04/22)
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- Carry over of impurities: A detailed exemplification for glycopyrrolate (NVA237)
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The original synthesis of glycopyrrolate (NVA237) was revised and shortened into an essentially one-pot process. Without isolating the intermediates, their purification became obsolete, thereby increasing the possibility of the carry over of impurities. For that reason, the actual, potential, and theoretical impurities of the starting materials cyclopentyl mandelic acid and 1-methyl-pyrrolidin-3-ol as well as byproducts which may occur during the synthesis were thoroughly investigated; furthermore, their transformation to possible impurities in the drug substance along the new synthetic route was performed to exclude them as actual impurities in the drug substance with certainty. The question is raised how detailed such investigation-which are fairly manageable for a simple product like glycopyrrolate-need to be.
- Allmendinger, Thomas,Bixel, Dominique,Clarke, Adrian,Di Geronimo, Laura,Fredy, Jean-Wilfried,Manz, Marco,Gavioli, Elena,Wicky, Regine,Schneider, Martin,Stauffert, Fabien J.,Tibi, Markus,Valentekovic, Darko
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supporting information
p. 1754 - 1769
(2013/01/15)
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- Regioselectivity of bromofluorination of functionalized 1-alkenes
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The regiochemistry of bromofluorinations of 1-alkenes with the combination of N-bromosuccinimide and amine/HF reagents mainly depends on the character of functional groups in the neighborhood of the double bond and only weakly from the fluorinating agent. While mono-substituted terminal alkenes mainly yield Markovnikov-oriented products, electron withdrawing groups in allylic or homoallylic position to the double bond destabilize carbenium centers in 2-position. Consequently, the part of anti-Markovnikov-oriented bromofluorides increases. Besides, with dropping reactivity of alkenes, the formation of dibromides becomes a competitive side reaction of bromofluorination. The extent of this process depends on the nature of the amine/HF reagent. This reaction is most important in case of the more nucleophilic trimethylamine bishydrofluoride, while this process is neglectible with pyridinium poly(hydrogen fluoride) (Olah's reagent).
- Lübke, Martin,Skupin, Rolf,Haufe, Günter
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p. 125 - 133
(2007/10/03)
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