[14657-22-8]  · C6H12Si  · (Trimethylsilyl)allene  · (MW 112.27)

(propargylic anion equivalent;2-4 substrate for ene reaction5)

Alternate Name: trimethyl-1,2-propadienylsilane.

Physical Data: bp 90-93 °C.

Solubility: sol CH2Cl2, benzene, most organic solvents.

Form Supplied in: colorless liquid; not commercially available.

Analysis of Reagent Purity: IR (tf) 2955, 2900, 1935, 1250, 1210, 1055, 840, 800, 750, and 690 cm-1; 1H NMR (60 MHz, CDCl3) d 0.15 (s, 9H), 4.27 (d, 2H, J = 7.7), 4.88 (dd, 1H, J = 6.6, 7.7).4b

Preparative Methods: two methods have been reported for the preparation of (trimethylsilyl)allene [(TMS)allene] (1). Reductive deoxygenation of the tosylhydrazone derivative affords the title compound in 51% yield.4b The tosylhydrazone is readily prepared from the corresponding aldehyde, which in turn is accessed by formylation of (trimethylsilyl)ethynylmagnesium bromide with DMF (eq 1).6 (TMS)allene has also been prepared by flash vacuum pyrolysis of methyl (trimethylsilyl)propargyl ether, which is obtained from silylation of methyl propargyl ether (eq 2).7

Purification: distillation at atmospheric pressure.4b

Handling, Storage, and Precautions: stable indefinitely when stored under nitrogen in the refrigerator.

Propargylic Anion Equivalent.

(TMS)allene reacts with electrophiles at the C-3 position in an SE2 process analogous to electrophilic substitution reactions of allyl- and propargylsilanes.8 For example, upon treatment with trimethylsilyl chlorosulfonate or Sulfur Trioxide-1,4-Dioxane, (TMS)allene yields silyl esters of sulfonic acids (eq 3).2 (TMS)allene undergoes conjugate addition with a,b-unsaturated acyl cyanides to yield d,ε-acetylenic acyl cyanides.3

Particularly important is the reaction of (TMS)allene with aldehydes and ketones, which provides a convenient route to secondary and tertiary homopropargylic alcohols, respectively. Treatment of (1) (1.1-1.5 equiv) with a mixture of carbonyl compound and 1.1-1.5 equiv of Titanium(IV) Chloride in methylene chloride produces mixtures of homopropargylic alcohols and (trimethylsilyl)vinyl chlorides. Exposure of the crude reaction product to 2.5 equiv of Potassium Fluoride in DMSO9 then furnishes the desired homopropargylic alcohols (eq 4).4

Several alternative reagents function as propargylic anion equivalents.10 Homopropargylic alcohols can be prepared by the addition of allenylboronate esters to aldehydes (though not to ketones).11 Brown has recently reported that 9-allenyl-9-BBN reacts with aldehydes and ketones to produce homopropargylic alcohols in good yields.12 Allenyllithium unfortunately combines with carbonyl compounds to afford mixtures of allenic and acetylenic alcohols.13 Allenylmagnesium bromide reacts with carbonyl compounds to furnish homopropargylic alcohols in poor yields; in some cases, mixtures of allenic and alkynic products are obtained.12 Diallenyltin dibromide, which is generated by reaction of propargyl bromide with tin metal in the presence of aluminum, reacts with both aldehydes and ketones to afford homopropargylic alcohols in good yield.14 Alternatively, triisopropylsilyl derivatives of these alkynes can be prepared by the reaction of the lithium derivative of 1-(triisopropylsilyl)propyne with ketones and aldehydes by using the procedure described by Corey and Rucker.15 Trimethylsilyl analogs of these alkynes have been prepared using the Reformatsky reagent derived from trimethylsilylpropargyl bromide: zinc-mediated condensation of trimethylsilylpropargyl bromide with aldehydes and ketones delivers homopropargylic alcohols (eq 5).16

Synthesis of Silylacetylenes via Ene Reaction.

(TMS)allene undergoes ene reactions with 4-Phenyl-1,2,4-triazoline-3,5-dione and other reactive enophiles to give silylacetylenes.5

Related Reagents.

Allenyllithium; 1-Methyl-1-(trimethylsilyl)allene; Allyltrimethylsilane; Propargylmagnesium Bromide; 3-Trimethylsilyl-1-propyne.

1. Review: Panek, J. S. COS 1991, 2, 579.
2. Bourgeois, P.; Calas, R.; Merault, G. JOM 1977, 141, 23.
3. (a) Jellal, A.; Santelli, M. TL 1980, 21, 4487. (b) Santelli, M.; Abed, D. E.; Jellal, A. JOC 1986, 51, 1199.
4. (a) Danheiser, R. L.; Carini, D. J. JOC 1980, 45, 3925. (b) Danheiser, R. L.; Carini, D. J.; Fink, D. M.; Basak, A. T 1983, 39, 935. (c) Danheiser, R. L.; Carini, D. J.; Kwasigroch, D. A. JOC 1986, 51, 3870.
5. Laporterie, A.; Dubac, J.; Manuel, G.; Deleris, G.; Kowalski, J.; Dunogues, J.; Calas, R. T 1978, 34, 2669.
6. Komarov, N. V.; Yarosh, O. G.; Astaf'eva, L. N. JGU 1966, 36, 920.
7. Hopf, H.; Naujoks, E. TL 1988, 29, 609.
8. See: ref. 1; Fleming, I. COS 1991, 2, 563; Fleming, K.; Dunogues, J.; Smithers, R. OR 1989, 37, 57.
9. Cunico, R. F.; Dexheimer, E. M. JACS 1972, 94, 2868.
10. For reviews of the chemistry of propargylic anion equivalents, see: (a) Yamamoto, H. COS 1991, 2, 81. (b) Epsztein, R. In Comprehensive Carbanion Chemistry; Buncel, E., Durst, T., Eds.; Elsevier: Amsterdam, 1984; Part B, pp 107-176. (c) Moreau, J.-L. In The Chemistry of Ketenes, Allenes, and Related Compounds; Patai, S., Ed.; Wiley: New York, 1978; pp 343-381.
11. (a) Favre, E.; Gaudemar, M. JOM 1974, 76, 297. (b) Favre, E.; Gaudemar, M. JOM 1974, 76, 305. (c) Haruta, R.; Ishiguro, M.; Ikeda, N.; Yamamoto, H. JACS 1982, 104, 7667.
12. Brown, H. C.; Khire, U. R.; Racherla, U. S. TL 1993, 34, 15, and references therein.
13. For example, see: Clinet, J.-C.; Linstrumelle, G. S 1981, 875.
14. Nokami, J.; Tamaoka, T.; Okawara, R. CL 1984, 1939.
15. Corey, E. J.; Rucker, C. TL 1982, 23, 719.
16. Daniels, R. G.; Paquette, L. A. TL 1981, 22, 1579.

Katherine L. Lee & Rick L. Danheiser

Massachusetts Institute of Technology, Cambridge, MA, USA

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