title: Improved synthesis of aryltrialkoxysilanes via treatment of aryl Grignard or lithium reagents with tetraalkyl orthosilicates.
abstract: General reaction conditions for the synthesis of aryl(trialkoxy)silanes from aryl Grignard and lithium reagents and tetraalkyl orthosilicates (Si(OR)(4)) have been developed. Ortho-, meta-, and para-substituted bromoarenes underwent efficient metalation and silylation at low temperature to provide aryl siloxanes. Mixed results were obtained with heteroaromatic substrates: 3-bromothiophene, 3-bromo-4-methoxypyridine, 5-bromoindole, and N-methyl-5-bromoindole underwent silylation in good yield, whereas a low yield of siloxane was obtained from 2-bromofuran, and 2-bromopyridine failed to give silylated product. The synthesis of siloxanes via organolithium and magnesium reagents was limited by the formation of di- and triarylated silanes (Ar(2)Si(OR)(2) and Ar(3)SiOR, respectively) and dehalogenated (Ar-H) byproducts. Silylation at low temperature gave predominantly monoaryl siloxanes, without requiring a large excess of the electrophile. Optimal reaction conditions for the synthesis of siloxanes from aryl Grignard reagents entailed addition of arylmagnesium reagents to 3 equiv of tetraethyl- or tetramethyl orthosilicate at -30 degrees C in THF. Aryllithium species were silylated using 1.5 equiv of tetraethyl- or tetramethyl orthosilicate at -78 degrees C in ether.
authors.affiliation: Department of Chemistry and Biochemistry, University of Maryland, College Park, Maryland 20742, USA.
authors.forename: Amy S
authors.initials: AS
authors.lastname: Manoso
authors.forename: Chuljin
authors.initials: C
authors.lastname: Ahn
authors.forename: Arash
authors.initials: A
authors.lastname: Soheili
authors.forename: Christopher J
authors.initials: CJ
authors.lastname: Handy
authors.forename: Reuben
authors.initials: R
authors.lastname: Correia
authors.forename: W Michael
authors.initials: WM
authors.lastname: Seganish
authors.forename: Philip
authors.initials: P
authors.lastname: Deshong
mesh_terms: D002384:Catalysis; D007202:Indicators and Reagents / Q000737:chemistry; D008094:Lithium / Q000737:chemistry; D008274:Magnesium / Q000737:chemistry; D008968:Molecular Conformation; D015394:Molecular Structure; D009942:Organometallic Compounds / Q000737:chemistry*; D010165:Palladium / Q000737:chemistry; D012821:Silanes / Q000138:chemical synthesis*; D017640:Silicates / Q000737:chemistry*
chemical_list: D007202:Indicators and Reagents; D009942:Organometallic Compounds; D012821:Silanes; D017640:Silicates; D010165:Palladium; D008094:Lithium; D008274:Magnesium