Triethoxysilane

Introduction

Triethoxysilane (TES) is an important chemical reagent in the synthesis of various organosilicon compounds. It is a colourless transparent liquid (bp 134–135 °C) with a characteristic ether odour. Triethoxysilane is an organosilane and has been widely used in organic synthesis as a mild reducing agent. It has been used for asymmetric hydrosilylation of ketones in order to obtain the corresponding alcohols.[1] Additionally, (EtO)₃SiH is applied as silylation reagent in regio- and stereoselective hydrosilylations.[2] It is able to cleave a C–C bond of the four-membered ring of biphenylene forming the corresponding 2-silylbiphenyls.[3] TES is also used in reductive etherification of aldehydes in the presence of the catalyst system InCl₃/TMSCl.[4]

Triethoxysilane is commercially available but it can also easily be synthesized in the reaction of trichlorosilane with anhydrous ethyl alcohol (Scheme [1]).[5]

Scheme 1

Table 1 Use of Triethoxysilane

(A) Beller and co-workers described a procedure for efficient reduction of tertiary amides. The reaction was carried out in the presence of inexpensive zinc catalyst with (EtO)3SiH under mild conditions.[6] Diverse functional groups present in the molecule (ester, ether, nitro, cyano, azo) are tolerated. The desired products were isolated in good to high yields.
(B) An efficient rhodium(I)-catalyzed reaction between arenediazonium tosylate salts and triethoxysilane led to aryltriethoxysilanes in good to high yields.[7] The synthesis was carried out in the presence of Bu4NI and Et3N.
(C) The preparation of various nitriles from primary carboxylic amides can be realized by iron-catalyzed [Et3NH, HFe3(CO)11] dehydration with triethoxysilane as dehydrating agents. The experiment was carried out using toluene as a solvent in 100 °C.[8]
(D) Ritter and co-workers reported a selective 1,2-hydrosilylation of conjugated dienes using triethoxysilane in the presence of catalytic amounts of platinum precatalyst. The catalyst was activated with methylmagnesium chloride (MeMgCl) at –45 °C, then (EtO)3SiH and diene were added. The mixture was heated to 50 °C. The product was formed with high selectivity.[9]
(E) Organosilanes are convenient reagents in the selective reduction of nitroarenes. The corresponding aniline was formed with (EtO)3SiH in the presence of a catalyst consisting of FeBr2 and Ph3P. The desired product was isolated in good yield (66%).[10]
(F) Riand and co-workers described the stereodivergent synthesis of polysubstituted enynes, which are useful building blocks. Vinylsiloxanes (Z)-2 and (E)-2 were obtained in high yields with an α/β selectivity of 80:20. These products were then converted into trisubstituted enynes, which were isolated with full retention of the stereochemistry.[11]
(G) The asymmetric silylcyclization of 1,6-enynes with (EtO)3SiH was carried out in the presence of a rhodium catalyst generated in situ.[12] It was observed that these reactions provide optically active silylalkylidene cyclopentane and pyrrolidine derivatives. These products were formed in good yields and with high enantioselectivities.
(H) (EtO)3SiH can be applied as a mild reducing agent for catalytic reductive dehydration of tertiary amide to the corresponding enamine catalyzed by potassium tert-butoxide (t-BuOK).[13] The reaction leading to the enamine proceeded with high conversion ratio.

• References

• 1 Liu S, Peng J, Yang H, Bai Y, Li J, Lai G. Tetrahedron 2012; 68: 1371
• 2 Ding S, Song L, Chung LW, Zhang X, Sun J, Wu Y. J. Am. Chem. Soc. 2013; 135: 13835
• 3 Matsuda T, Kirikae H. Organometallics 2011; 30: 3923
• 4 Yang M, Xu L, Qiu H, Lai G, Jiang J. Tetrahedron Lett. 2008; 49: 253
• 5 Friedel C, Ladenburg A. Justus Liebigs Ann. Chem. 1867; 143: 118
• 6 Das S, Addis D, Zhou S, Junge K, Beller M. J. Am. Chem. Soc. 2010; 132: 1770
• 7 Tang ZY, Zhang Y, Wang T, Wang W. Synlett 2010; 5: 804
• 8 Zhou S, Addis D, Das S, Junge K, Beller M. Chem. Commun. 2009; 32: 4883
• 9 Parker SE, Börgel J, Ritter T. J. Am. Chem. Soc. 2014; 136: 4857
• 10 Junge K, Wendt B, Shaikh N, Beller M. Chem. Commun. 2010; 46: 1769
• 11 Cornelissen L, Lefrancq M, Riant O. Org. Lett. 2014; 16: 3024
• 12 Fan B, Xie J, Li S, Wang L, Zhou Q. Angew. Chem. Int. Ed. 2007; 46: 1275
• 13 Volkov A, Tinnis F, Adolfsson H. Org. Lett. 2014; 16: 680