Improved synthesis of aryltrialkoxysilanes via treatment of aryl Grignard or lithium reagents with tetraalkyl orthosilicates.
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.
Manoso
Amy S
AS
Department of Chemistry and Biochemistry, University of Maryland, College Park, Maryland 20742, USA.
Ahn
Chuljin
C
Soheili
Arash
A
Handy
Christopher J
CJ
Correia
Reuben
R
Seganish
W Michael
WM
Deshong
Philip
P
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*
D007202:Indicators and Reagents; D009942:Organometallic Compounds; D012821:Silanes; D017640:Silicates; D010165:Palladium; D008094:Lithium; D008274:Magnesium