Halogenation of alkenylaluminums by sulfonyl chlorides and bromides

Ilfir Ramazanov,Rita Kadikova,Usein Dzhemilev

doi:10.3390/ecsoc-15-00634

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.

Highlights

One of the most widely used methods for the functionalization of organometallic compounds is electrophilic halogenation
First of all we planned to explore the reaction of substituted alkenylaluminums that were prepared by various methods with sulfonyl halides, which we believed to be effective sources of electrophilic halogen
We examined the reactivity of alkenylaluminums prepared in situ by hydroand carboalumination of alkynes

Summary

Introduction

One of the most widely used methods for the functionalization of organometallic compounds is electrophilic halogenation. First of all we planned to explore the reaction of substituted alkenylaluminums that were prepared by various methods with sulfonyl halides, which we believed to be effective sources of electrophilic halogen. We found that alkenylaluminums obtained in Zr-catalyzed methylalumination of terminal alkynes (1-octyne, phenylacetylene) react with mesyl chloride or mesyl bromide for 15 minutes at room temperature in dichloromethane to give corresponding alkenyl halides 1a,b or 2a,b in high yield (Scheme 1).

Results

Conclusion