Electrophilic Addition of XY Reagents to Alkenes and Alkynes

Abstract

Electrophilic addition of the halogens and related X Y reagents to alkenes and alkynes has been a standard procedure since the beginning of modern organic chemistry. 1 Anti electrophilic bromination of such simple compounds as cyclohexene and ( E )- and ( Z )-2-butene, and variants of this reaction when water or methanol are solvents (formation of halohydrin or their methyl ethers, respectively), are frequently employed as prototype examples of stereospecific reactions in elementary courses in organic chemistry. A simple test for unsaturation involves addition of a dilute solution of bromine in CCl 4 to the compound in question: alkenes and alkynes discharge the color. Prior to the development of modern analytical methods, quantitative analysis of alkenes was performed by titration with bromine, thiocyanogen or related interhalogens. Spurred by interest in biologically active organofluorine compounds, methods have recently been developed for controlled addition of highly reactive elemental fluorine and fluorine-containing interhalogens to alkenes and alkynes. Regio- and stereo-specific addition of sulfenyl halides and reagents with nitrogen–halogen bonds to alkenes and alkynes have been used for many years for controlled introduction of sulfur and nitrogen, respectively, as well as for other more general synthetic purposes. More recently, electrophiles containing selenium and tellurium have been added to the list of synthetically useful reagents that undergo stereocontrolled addition to π-bonds.