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Halogenation of alkenylaluminums by sulfonyl chlorides and bromides
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1  Institute of Petrochemistry and Catalysis of Russian Academy of Sciences, 141 Prospekt Oktyabrya, Ufa 450075, Russian Federation

Abstract: We have explored the reaction of substituted alkenylaluminums that were prepared by various methods with sulfonyl halides, which we believed to be effective sources of electrophilic halogen. Alkenylaluminums obtained in Zr-catalyzed methylalumination of terminal alkynes react with sulfonyl chlorides and bromides to give corresponding alkenyl halides in high yield. Cycloalumination of 1-decyne and phenylacetylene affords aluminacyclopent-2-enes, which react with 1 equivalent of sulfonyl chlorides and bromides to give after deuterolysis alkenyl halides in high yield. The halogenation proceeds regioselectively only at the sp2-hybridized carbon atom and with the retention of the configuration of the double bond. To our surprise, b-substituted vinylaluminums that were obtained by hydroalumination of terminal alkynes (1-octyne, phenylacetylene) by DIBAL-H do not react with sulfonyl halides (MsCl, TsCl, MsBr). Thus, the sulfonyl chlorides and bromides are more convenient halogenation agents for b,b- and a,b,b-substituted vinylaluminums that were prepared by Zr-catalyzed methylalumination and cycloalumination compared to NCS and NBS, which is manifested in the facts that: a) the reaction proceeds at room temperature; b) the reaction does not require the use of ether solvent (moreover, the latter inhibits the halogenation), c) higher regioselectivity for the bromination of aluminacyclopent-2-enes is observed.
Keywords: carboalumination, halogenation, alkenylaluminums