title: Catalyst-Free Formal Thioboration to Synthesize Borylated Benzothiophenes and Dihydrothiophenes.
abstract: The first ring-forming thioboration reaction of C-C π bonds is reported. This catalyst-free method proceeds in the presence of a commercially available external electrophilic boron source (B-chlorocatecholborane) in good to high yields. The method is scalable and tolerates a variety of functional groups that are intolerant of other major borylation methods. The resulting borylated benzothiophenes participate in a variety of in situ derivatization reactions, showcasing that these borylated intermediates do not need to be isolated prior to downstream functionalization. This methodology has been extended to the synthesis of borylated dihydrothiophenes. Mechanistic experiments suggest that the operative mechanistic pathway is through boron-induced activation of the alkyne followed by electrophilic cyclization, as opposed to S-B σ bond formation, providing a mechanistically distinct pathway to the thioboration of C-C π bonds.
authors.affiliation: Department of Chemistry, University of California, Irvine, Irvine, CA, 92697, USA.
authors.forename: Darius J
authors.initials: DJ
authors.lastname: Faizi
authors.affiliation: Department of Chemistry, University of California, Irvine, Irvine, CA, 92697, USA.
authors.forename: Ashlee J
authors.initials: AJ
authors.lastname: Davis
authors.affiliation: Department of Chemistry, University of California, Irvine, Irvine, CA, 92697, USA.
authors.forename: Fiach B
authors.initials: FB
authors.lastname: Meany
authors.affiliation: Department of Chemistry, University of California, Irvine, Irvine, CA, 92697, USA. blums@uci.edu.
authors.forename: Suzanne A
authors.initials: SA
authors.lastname: Blum
mesh_terms: D000480:Alkynes / Q000737:chemistry; D001895:Boron / Q000737:chemistry*; D002244:Carbon / Q000737:chemistry; D018360:Crystallography, X-Ray; D003500:Cyclization; D008968:Molecular Conformation; D011789:Quantum Theory; D013876:Thiophenes / Q000138:chemical synthesis / Q000737:chemistry*
chemical_list: D000480:Alkynes; D013876:Thiophenes; C088015:benzothiophene; D002244:Carbon; D001895:Boron
keywords: C−C activation; boron; cyclization; sulfur; sulfur heterocycles