[18395-90-9]  · C8H18Cl2Si  · Di-t-butyldichlorosilane  · (MW 213.22)

(reagent for the protection of diols; used as a silylene precursor)

Physical Data: mp -15 °C; bp 190 °C/729 mmHg; d 1.009 g cm-3.

Solubility: sol most common organic solvents.

Form Supplied in: liquid.

Preparative Methods: can be conveniently prepared by chlorination of di-t-butylsilane (CCl4/PdCl2 (cat), 85%)1,2 but various other methods of preparation have been reported.3-6

Purification: distillation.

Handling, Storage, and Precautions: moisture sensitive; reacts with hydroxylic solvents, corrosive; lachrymator. Use in a fume hood.

Protection of Alcohols.

The presence of the bulky t-butyl groups in di-t-butyldichlorosilane has been found to increase the Si-C bond lengths slightly and to widen the CSiC bond angles by 11.1° relative to Dichlorodimethylsilane as determined by electron diffraction and molecular mechanics calculations.7

The di-t-butylsilylene protecting group for diols was introduced by Trost and Caldwell4 and used in a total synthesis of deoxypillaromycinone.5 It is introduced by the reaction of di-t-butyldichlorosilane with a 1,2- or 1,3-diol in acetonitrile in the presence of Triethylamine and 1-Hydroxybenzotriazole (HOBt) at 45-90 °C (eq 1). For a related, highly reactive reagent see Di-t-butylsilyl Bis(trifluoromethanesulfonate).

When at least one of the hydroxy groups is phenolic or primary, reactions proceed smoothly at 25-65 °C, but when both hydroxy groups are secondary, more forcing conditions (95 °C, sealed tube) are required. In all cases, yields range from 64% to 85%. No examples have been reported with tertiary alcohols. Pyridinium Poly(hydrogen fluoride) is used for deprotection and under those conditions a t-butyldimethylsilyl ether and a b-hydroxy ketone are unaffected (eq 2).

This protecting group has seen limited use but has been applied in ribonucleoside chemistry.8-10 The reagent reacts slowly with nucleosides in the presence of imidazole/DMF but formation of the more reactive di-t-butylsilyl dinitrate in situ, followed by addition of cytidine, results in a protected 3,5-silylene derivative in excellent yield (90%) (eq 3). The protecting group can be removed conveniently with tributylamine hydrofluoride.11

A one-pot procedure has been reported for the selective protection of a secondary alcohol over a primary alcohol in a 1,3-diol in 2-deoxynucleosides (eq 4).12,13

Derivatization of Diols and Hydroxy Acids.

Di-t-butyldichlorosilane has been used to derivatize a-hydroxy acids, b-hydroxy acids, alkylsalicyclic acids, anthranilic acid, catechols, and 1,2- and 1,3-diols for analysis by gas chromatography-electron impact mass spectrometry (eq 5).14,15 These derivatives are useful for separation. The major fragmentation is that of Si-C bonds. The 1,2-diol in the antibiotic sorangicin has also been derivatized with di-t-butyldichlorosilane.16

Silylene Precursor.

Di-t-butyldichlorosilane can be reduced using Lithium/THF to give a putative silylene derivative that will react with double bonds to give 1,1-silirane derivatives17-19 or react with triethylsilane to give an Si-H insertion product (eq 6).17

Reaction of di-t-butyldichlorosilane with Lithium Naphthalenide in DME gives compound (1) which upon irradiation gives, in addition to naphthalene, tetra-t-butyldisilene that subsequently reacts with 2,3-dimethylbutadiene to give a Diels-Alder adduct along with a product arising from an ene reaction (eq 7).20

Reduction of di-t-butyldichlorosilane with lithium in THF at 0 °C in the presence of an excess of Dichlorodimethylsilane gives compound (2).21 Reaction of di-t-butyldichlorosilane with lithium and 1,4-diaza-1,3-butadienes gives 1,3-diaza-2-sila-4-cyclopentenes (eq 8).22

Other Substitution Reactions.

The chlorine atoms in di-t-butyldichlorosilane can be replaced with various nucleophiles. Di-t-butyldifluorosilane has been prepared by using SbF3,23,24 ZnF2,25 or (NH4)2SiF6.26,27 Reaction of di-t-butyldichlorosilane with Lithium Aluminum Hydride gives di-t-butylsilane28 and reaction with Sodium Azide gives di-t-butyldiazidosilane; upon irradiation this gives a putative di-t-butylsilylene which undergoes various reactions depending on the conditions.29 Reactions of di-t-butyldichlorosilane with LiPHMe30 and LiPH231 yield (3) and (4), respectively.

Treatment of di-t-butyldichlorosilane with Trimethylsilyllithium gives di-(t-butyl)bis(trimethylsilyl)silane.32

1. Watanabe, H.; Ohkawa, T.; Muraoka, T.; Nagai, Y. CL 1981, 1321.
2. Watanabe, H.; Muraoka, T.; Kageyama, M.; Yoshizumi, K.; Nagai, Y. OM 1984, 3, 141.
3. Doyle, M. P.; West, C. T. JACS 1975, 97, 3777.
4. Trost, B. M.; Caldwell, C. G. TL 1981, 22, 4999.
5. Trost, B. M.; Caldwell, C. G.; Murayama, E.; Heissler, D. JOC 1983, 48, 3252.
6. Graalmann, O.; Klingebiel, U. JOM 1984, 275, C1.
7. Forsyth, G. A.; Rankin, D. W. H. J. Mol. Struct. 1990, 222, 467.
8. Furusawa, K.; Ueno, K.; Katsura, T. CL 1990, 97.
9. Furusawa, K.; Katsura, T. TL 1985, 26, 887.
10. Furusawa, K.; Katsura, T.; Sakai, T.; Tsuda, K. Nucleic Acids Symp. Ser. 1984, 15, 41.
11. Furusawa, K. CL 1989, 509.
12. Furusawa, K.; Sakai, T.; Tsuda, K. Jpn. Kokai Tokkyo Koho 1988, 913.
13. Furusawa, K.; Sakai, T.; Tsuda, K. Kenkyu Hokou - Sen'i Kobunshi Zairyo Kenkyusho 1988, 158, 121.
14. Brooks, C. J. W.; Cole, W. J.; Barrett, G. M. J. Chromatogr. 1984, 315, 119.
15. Brooks, C. J. W.; Cole, W. J. Analyst 1985, 110, 587.
16. Hoefle, G.; Jansen, R.; Schummer, D. Ger. Offen. 3 930 950, 1991.
17. Boudjouk, P.; Samaraweera, U.; Sooriyakumaran, R.; Chrusciel, J.; Anderson, K. R. AG(E) 1988, 27, 1355.
18. Weidenbruch, M.; Lesch, A.; Marsmann, H. JOM 1990, 385, C47.
19. Boudjouk, P.; Black, E.; Kumarathasan, R. OM 1991, 10, 2095.
20. Masamune, S.; Murakami, S.; Tobita, H. OM 1983, 2, 1464.
21. Helmer, B. J.; West, R. JOM 1982, 236, 21.
22. Weidenbruch, M.; Lesch, A.; Peters, K. JOM 1991, 407, 31.
23. Weidenbruch, M.; Peter, W. AG(E) 1975, 14, 642.
24. Weidenbruch, M.; Pesel, H.; Peter, W; Steichen, R. JOM 1977, 141, 9.
25. Rempfer, B.; Oberhammer, H.; Auner, N. JACS 1986, 108, 3893.
26. Damrauer, R.; Simon, R. A. OM 1988, 7, 1161.
27. Auner, N. Z. Anorg. Allg. Chem. 1988, 558, 87.
28. Triplett, K.; Curtis, M. D. JOM 1976, 107, 23.
29. Welsh, K. M.; Michl, J.; West, R. JACS 1988, 110, 6689.
30. Fritz, G.; Uhlmann, R. Z. Anorg. Allg. Chem. 1978, 442, 95.
31. Fritz, G.; Biastoch, R. Z. Anorg. Allg. Chem. 1986, 535, 63.
32. Becker, G.; Hartmann, H. M.; Muench, A.; Riffel, H. Z. Anorg. Allg. Chem. 1985, 530, 29.

Snorri T. Sigurdsson & Paul B. Hopkins

University of Washington, Seattle, WA, USA

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