The use of a new class of unsymmetrical cinchona alkaloid-based, phthalazine-bridged organocatalysts enabled the highly enantioselective dichlorination of unfunctionalized alkenes. In combination with the electrophilic chlorinating agent 1,3-dichloro-5,5dimethylhydantoin (DCDMH) and triethylsilyl chloride TES-Cl as source of nucleophilic chloride, 1-aryl-2-alkyl alkenes were dichlorinated with enantioselectivities up to 94:6 er. Initial mechanistic investigations suggest that no free chlorine is formed and, by replacement of the chloride by fluoride, enantioselective chlorofluorinations of alkenes are possible.
The dihalogenation of alkenes is one of the classic reactions in organic chemistry and a prime example of an electrophilic addition reaction. The often observed anti‐selectivity in this addition reaction can be explained by the formation of a haliranium‐ion intermediate. Although dihalogenations have been studied for more than a century, the development of reagent‐controlled, enantioselective dihalogenation has proved to be very difficult. Only recently, significant progress has been achieved. In this review, an overview on current method development in enantioselective dihalogenation is provided and mechanistic aspects that render this transformation challenging are discussed.
Der Einsatz einer neuen Klasse unsymmetrischer Chinaalkaloid‐basierter, Phthalazin‐verbrückter Organokatalysatoren ermöglichte die hoch enantioselektive Dichlorierung von unfunktionalisierten Alkenen. In Kombination mit dem elektrophilen Chlorierungsmittel 1,3‐Dichlor‐5,5‐dimethylhydantoin (DCDMH) und Triethylsilylchlorid (TES‐Cl) als nukleophiler Chloridquelle wurden 1‐Aryl‐2‐alkylalkene mit Enantioselektivitäten von bis zu 94:6 er dichloriert. Erste mechanistische Untersuchungen deuten darauf hin, dass kein freies Chlor gebildet wird. Das Ersetzen von Chlorid durch Fluorid ermöglichte die enantioselektive Chlorfluorierung von Alkenen.
Dihalogenation of alkenes is one of the classic reactions in organic chemistry and a prime example of an electrophilic addition reaction. Although being studied intensely, the development of reagent‐controlled, enantioselective dihalogenation is still challenging. Read more about current method development and mechanistic aspects in enantioselective dihalogenation in the Minireview by U. Hennecke et al. on page 4517.
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