Kinetics and mechanism of the racemic addition of trimethylsilyl cyanide to aldehydes catalysed by Lewis bases

Abstract

The mechanism by which four Lewis bases, triethylamine, tetrabutylammonium thiocyanate, tetrabutylammonium azide and tetrabutylammonium cyanide, catalyse the addition of trimethylsilyl cyanide to aldehydes is studied by a combination of kinetic and spectroscopic methods. The reactions can exhibit first or second order kinetics corresponding to three different reaction mechanisms. Spectroscopic evidence for the formation of hypervalent silicon species is obtained for reaction between all of the tetrabutylammonium salts and trimethylsilyl cyanide. The reactions are accelerated by the presence of water in the reaction mixture, an effect which is due to a change in the reaction mechanism from Lewis to Brønsted base catalysis. Tetrabutylammonium thiocyanate is shown to be an excellent catalyst for the synthesis of cyanohydrin trimethylsilyl ethers on a preparative scale.

1-Ethyl-3-methylimidazolium acetate as a highly efficient organocatalyst for cyanosilylation of carbonyl compounds with trimethylsilyl cyanide

“…In this respect, the development of efficient catalysts for the addition of TMSCN to carbonyl compounds has been the focal research point. As a consequence, various Lewis acids, Lewis bases, metal alkoxides, as well as inorganic salts have been successfully employed in promoting this transformation 3 12 13 14 15 16 17 18 19 20 21 22 23 24 .…”

Cyanidosilikate – Synthese und Struktur

“…Über neutrale binäre Si‐CN‐Verbindungen (z. B. Si‐CN und Si(CN) 2 ), die in einer Argonmatrix untersucht oder in der Hülle eines Sterns beobachtet wurden, weiß man wenig, obwohl cyanidhaltige Silane, wie das Cyantrimethylsilan (Me 3 Si‐CN), in der organischen Chemie für ihre vielseitige Verwendung als Cyanosilylierungsreagens in Kombination mit Lewis‐Säuren oder ‐Basen bekannt sind . Das höher substituierte Dicyandimethylsilan kann als Schutzgruppe verwendet werden, während das Tricyanmethylsilan noch nicht isoliert, aber vermutlich in situ in einer Reaktion von MeSiCl 3 mit KCN gebildet wird .…”

Theoretical Insights into Aluminum-Catalyzed Cyanosilylation of Aldehydes and Ketones

“…As trimethylsilyl cyanide (TMSCN) is easy to handle and exhibits lower Si–C bond dissociation energy, it has been widely utilized as a cyanide source with various catalysts for the compelling conversion of carbonyl compounds into the corresponding cyanohydrin trimethylsilyl ethers. − The high atom economy without resulting side reactions also broadens the scope of TMSCN in cyanosilylation reactions. Based on recent reports, cyanosilylation of aldehydes in the absence of catalysts requires high temperature and reaction time, while ketones showed poor reactivity under similar reaction conditions .…”