Halogenation of alkenylaluminums by sulfonyl chlorides and bromides

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.