A mild method for the replacement of a hydroxyl group by halogen: 2. unified procedure and stereochemical studies
N,N-Dimethyl- and N,N-diisopropyl-1-halo-2-methyl-l-propenylamines are readily available reagents for the mild deoxyhalogenation of alcohols and hydroxyacids. In this study we showed that the reactivity of the reagents can be tuned by varying the size of the alkyl groups on the reagents: the replacement of methyl by isopropyl groups led to a significant increase of reactivity. We then described a unified procedure for all deoxyhalogenations using the readily available α-chloroenamines as reagents with (bromination, iodination) or without (chlorination) an alkaline bromide or iodide. Finally, we showed that deoxyhalogenation reactions of secondary alcohols were highly stereospecific and generally occurred with inversion of configuration.
A mild method for the replacement of a hydroxyl group by halogen. 1. Scope and chemoselectivity
α-Chloro-, bromo- and iodoenamines, which are readily prepared from the corresponding isobutyramides have been found to be excellent reagents for the transformation of a wide variety of alcohols or carboxylic acids into the corresponding halides. Yields are high and conditions are very mild thus allowing for the presence of sensitive functional groups. The reagents can be easily tuned allowing therefore the selective monohalogenation of polyhydroxylated molecules. The scope and chemoselectivity of the reactions have been studied and reaction mechanisms have been proposed.
SYNTHESIS OF ALKYL HALIDES UNDER NEUTRAL CONDITIONS
Primary and secondary alcohols are efficiently converted to the corresponding alkyl halides under neutral conditions.
Munyemana, Francois,Frisque-Hesbain, Anne-Marie,Devos, Alain,Ghosez, Leon
p. 3077 - 3080
(2007/10/02)
PREPARATION OF GLYCOSYL HALIDES UNDER NEUTRAL CONDITIONS
The anomeric hydroxyl group of various furanose and pyranose hemiacetals can be replaced by a fluorine, chlorine, bromine or iodine atom under neutral conditions using haloenamines.
Ernst, Beat.,Winkler, Tammo.
p. 3081 - 3084
(2007/10/02)
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