title: Catalytic, Stereoselective Dihalogenation of Alkenes: Challenges and Opportunities.
abstract: Although recent years have witnessed significant advances in the development of catalytic, enantioselective halofunctionalizations of alkenes, the related dihalogenation of olefins to afford enantioenriched vicinal dihalide products remains comparatively underdeveloped. However, the growing number of complex natural products bearing halogen atoms at stereogenic centers has underscored this critical gap in the synthetic chemist's arsenal. This Review highlights the selectivity challenges inherent in the design of enantioselective dihalogenation processes, and formulates a mechanism-based classification of alkene dihalogenations, including those that may circumvent the "classical" haliranium (or alkene-dihalogen π-complex) intermediates. A variety of metal and main group halide reagents that have been used for the dichlorination or dibromination of alkenes are discussed, and the proposed mechanisms of these transformations are critically evaluated.
authors.affiliation: EaStCHEM, School of Chemistry, University of Edinburgh, Edinburgh, EH9 3JJ (UK).
authors.forename: Alexander J
authors.initials: AJ
authors.lastname: Cresswell
authors.affiliation: Organic Chemistry, Institute of Chemical and Engineering Sciences, A*STAR, Singapore 138667 (Singapore).
authors.forename: Stanley T-C
authors.initials: ST
authors.lastname: Eey
authors.affiliation: Department of Chemistry, University of Illinois at Urbana-Champaign, Urbana, IL 61801 (USA) http://www.scs.illinois.edu/denmark. sdenmark@illinois.edu.
authors.forename: Scott E
authors.initials: SE
authors.lastname: Denmark
mesh_terms: D000475:Alkenes / Q000737:chemistry*; D002384:Catalysis; D006219:Halogens / Q000737:chemistry*; D013237:Stereoisomerism
chemical_list: D000475:Alkenes; D006219:Halogens
keywords: alkenes; catalysis; dihalogenation; enantioselective  synthesis; reaction  mechanisms