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.

Synthesis and structural characterization of functionalized cyclotetrasiloxane rings [4-RC6H4Si(O)OR′]4 (R=Cl, Br, CHCH2, CH2Cl; R′=Na, SiMe3) as scaffolds for the synthesis of models of a silica bound monolayer of fluorescent or second order NLO active organic chromophores

“…All reactions were performed under nitrogen atmosphere. The 4-(triethoxysilyl)bromobenzene [10] and 4-(trietoxysilyl)styrene [11] were prepared making some modifications to the procedure reported in the literature, 4-(triethoxysilyl)chloromethylbenzene was prepared by the correspondent trimethoxysilyl derivative by exchange reaction with anhydrous EtOH [18]. 1 H and 29 Si NMR spectra were recorded with a Bruker Avance DRX 400 and DRX 500 spectrometers in CDCl 3 and DMSO-d 6 as solvents.…”

“…The starting reagent 4-(triethoxysilyl)bromobenzene was prepared in good yield (66%) from 1,4-dibromobenzene, making some modifications to the known general procedure (see Section 4) [10]. Equally the 4-(triethoxysilyl)styrene was prepared in high yield (75%) from 4-bromostyrene, making some modifications to the known procedure (see Section 4) [11].…”

Preparation of 1,1-disubstituted silacyclopentadienes

“…Treatment of 1,1-dichlorosilole 2 in diethyl ether with (4-MeOC 6 H 4 )MgBr [22] prepared from 4-bromoanisole afforded the 1,1-diarylsilole 8 in 82% yield (Eq. (2)).…”

Diphenylphosphinite ionic liquid (IL-OPPh2): A solvent and ligand for palladium-catalyzed silylation and dehalogenation reaction of aryl halides with triethylsilane

“…Traditional synthetic routes to arylsilanes consist of the reaction of silicon electrophiles with aryl Grignard or aryllithium compounds [2][3][4]. Drawback of this methodology is the limited number of substrates available.…”