Manoso Amy S, Ahn Chuljin, Soheili Arash, Handy Christopher J, Correia Reuben, Seganish W Michael, Deshong Philip
Department of Chemistry and Biochemistry, University of Maryland, College Park, Maryland 20742, USA.
J Org Chem. 2004 Nov 26;69(24):8305-14. 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 (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.
已开发出由芳基格氏试剂、锂试剂和原硅酸四烷基酯（Si(OR)₄）合成芳基（三烷氧基）硅烷的一般反应条件。邻位、间位和对位取代的溴代芳烃在低温下能高效地进行金属化和硅烷化反应，生成芳基硅氧烷。杂芳族底物的反应结果不一：3-溴噻吩、3-溴-4-甲氧基吡啶、5-溴吲哚和N-甲基-5-溴吲哚能以良好的产率进行硅烷化反应，而从2-溴呋喃得到的硅氧烷产率较低，2-溴吡啶则未能得到硅烷化产物。通过有机锂试剂和镁试剂合成硅氧烷受到二芳基硅烷（Ar₂Si(OR)₂）和三芳基硅烷（Ar₃SiOR）的形成以及脱卤副产物（Ar-H）的限制。低温下的硅烷化反应主要生成单芳基硅氧烷，无需大量过量的亲电试剂。由芳基格氏试剂合成硅氧烷的最佳反应条件是在-30℃的四氢呋喃中，将芳基镁试剂加入到3当量的原硅酸四乙酯或原硅酸四甲酯中。芳基锂试剂在-78℃的乙醚中使用1.5当量的原硅酸四乙酯或原硅酸四甲酯进行硅烷化反应。
