[5158-09-8] · C4H6N2Si · Dicyanodimethylsilane · (MW 110.19)
Physical Data: mp 85-87 °C; bp 108-109 °C/54 mmHg.
Solubility: sol dichloromethane, chloroform; slightly sol ether.
Preparative Methods: dicyanodimethylsilane is conveniently prepared by the reaction of dibromodimethylsilane5 or Dichlorodimethylsilane6 with Silver(I) Cyanide. Lithium Cyanide,4 Sodium Cyanide,7 and Potassium Cyanide7 can also be used in place of silver cyanide. A method which uses Hydrogen Cyanide as a source of cyano groups8 and a procedure which utilizes transcyanation with Cyanotrimethylsilane have also been reported.9 Dicyanodimethylsilane is obtained as colorless crystals via these methods.
Handling, Storage, and Precautions: dicyanodimethylsilane reacts instantly with water to form highly toxic hydrogen cyanide and siloxane oligomers. Therefore it should be handled carefully in a fume hood. If possible, it is recommended that CH2Cl2 solutions of this reagent be transferred by using syringe techniques.
While enol silylations and cyanosilylations of b-diketones with cyanotrimethylsilane often give mixtures of products, the reactions with dicyanodimethylsilane give 5-cyano-2,6-dioxa-1-silacyclohex-3-enes in good yields (eq 1).1 For enolizable b-diketones, the concurrent silylation and cyanosilylation takes place immediately without catalysts. On the other hand, Zinc Iodide catalysis is effective for reactions with less easily enolizable b-diketones (eq 2). Methyl 2,4-dioxopentanoate also reacts with dicyanodimethylsilane to give the corresponding cyclic product.2 Treatment of the adducts in methanol (rt, overnight) furnishes the parent 1,3-diketones in good yields. Taking advantage of the stepwise nature of the methanolysis, a formal cyanosilylation can be achieved by treating the adduct with 1 equiv of methanol in dichloromethane at rt (eq 3).1
The reaction of dicyanodimethylsilane with diacetone alcohol occurs according to eq 4.1 The reaction, which is initiated at -78 °C, proceeds by way of the indicated cyanodimethylsilyl ether. When warmed to rt, the intermediate silyl ether cyclizes to give a mixture of the cyanosilylation product and the cyclic enol silyl ether. The cyanosilylation of secondary b-hydroxy ketones is highly diastereoselective (eq 5).3 After desilylation, the cyanohydrins are obtained with high syn selectivity (de > 95%). The stereochemical result is rationalized by assuming a silyl-bridged chair-type transition state. Dicyanodimethylsilane reacts readily with alcohols, with liberation of hydrogen cyanide, to give bis(alkoxy)silanes in high yields (eq 6).4
Dicyanodimethylsilane, dicyanodiethylsilane,7,10 dicyanodiphenylsilane,7,11 and dicyanomethylphenylsilane12 are a family of related R2Si(CN)2 reagents that can be used as protecting groups for bifunctional compounds. The silyl-protection of 1,2- and 1,3-diols with these dicyanosilanes is well documented, affording the corresponding five- and six-membered ring compounds (eqs 7 and 8).4 The reaction of dicyanomethylphenylsilane with ketones is reported to give biscyanosilylated products, but the yield is modest due to competitive aldol condensations.12
Osaka University, Japan