Improved Synthesis of Aryltrialkoxysilanes via Treatment of Aryl Grignard or Lithium Reagents with Tetraalkyl Orthosilicates

• Published in: Journal of organic chemistry Vol. 69; no. 24; pp. 8305 - 8314
• Main Authors: Manoso, Amy S, Ahn, Chuljin, Soheili, Arash, Handy, Christopher J, Correia, Reuben, Seganish, W. Michael, DeShong, Philip
• Format: Journal Article
• Language: English
• Published: WASHINGTON American Chemical Society 26.11.2004; Amer Chemical Soc
• Subjects: Catalysis; Chemistry; Chemistry, Organic; Exact sciences and technology; Indicators and Reagents - chemistry; Lithium - chemistry; Magnesium - chemistry; Molecular Conformation; Molecular Structure; Organic chemistry; Organometallic Compounds - chemistry; Organometalloidal and organometallic compounds; Palladium - chemistry; Physical Sciences; Preparations and properties; Science & Technology; Si derivatives; Silanes - chemical synthesis; Silicates - chemistry; HALIDES; SILICON-COMPOUNDS; CROSS-COUPLING REACTIONS; HYPERVALENT SILOXANE DERIVATIVES; PALLADIUM-CATALYZED SILYLATION; CHLORIDES; SUZUKI COUPLINGS; BROMIDES; ARYLTRIETHOXYSILANES; ORGANOSILICON COMPOUNDS; Organic synthesis; Grignard reagent; Lithium Organic compounds; Functionalization; Silicon Organic compounds; Organic silane; Magnesium Organic compounds; Chemical coupling; Organic silicate
• ISSN: 0022-3263; 1520-6904
• DOI: 10.1021/jo048667h

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 (Ar2Si(OR)2 and Ar3SiOR, 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 °C in THF. Aryllithium species were silylated using 1.5 equiv of tetraethyl- or tetramethyl orthosilicate at −78 °C in ether.