[5158-09-8]  · C4H6N2Si  · Dicyanodimethylsilane  · (MW 110.19)

(protecting reagent of b-diketones1,2 and b-hydroxy ketones,1,3 diols, and alcohols4)

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.

Reaction with b-Diketones.

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

Reaction with b-Hydroxy Ketones and Alcohols.

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

Dicyanodiethylsilane, Dicyanodiphenylsilane, and Dicyanomethylphenylsilane.

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

Related Reagents.

Di-t-butyldichlorosilane; Di-t-butylsilyl Bis(trifluoromethanesulfonate); Dichlorodimethylsilane.

1. Ryu, I.; Murai, S.; Shinonaga, A.; Horiike, T.; Sonoda, N. JOC 1978, 43, 780.
2. Foley, L. H. JOC 1985, 50, 5204.
3. Batra, M. S.; Brunet, E. TL 1993, 34, 711.
4. Mai, K.; Patil, G. JOC 1986, 51, 3545.
5. McBride, J. J., Jr.; Beachell, H. C. JACS 1952, 74, 5247.
6. Ryu, I.; Murai, S.; Horiike, T.; Shinonaga, A.; Sonoda, N. S 1978, 154.
7. Sukata, K. BCJ 1987, 60, 2257.
8. Hundeck, J. Z. Anorg. Allg. Chem. 1966, 345, 23.
9. Becu, C.; Anteunis, M. J. O. BSB 1987, 96, 115.
10. Earborn, C. JCS 1949, 2755.
11. Johns, I. B.; DiPiertro, H. R. JOC 1964, 29, 1970.
12. Neef, H. JPR 1974, 316, 817.

Ilhyong Ryu

Osaka University, Japan

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