[1000-62-0]  · C7H14OSi  · Ethoxy(trimethylsilyl)acetylene  · (MW 142.27)

(mild agent for conversion of carboxylic acids into carboxylic anhydrides;1 dehydrative condensation agent for carboxylic acids and amines and alcohols;2 trimethylsilylketene precursor;3 2p component in cycloaddition reactions4)

Physical Data: bp 57 °C/34 mmHg; d 0.828 g cm-3.

Solubility: insol H2O; freely sol most common solvents.

Form Supplied in: colorless liquid; widely available.

Preparative Methods: by silylation of Ethoxyacetylene.1,3,5

Handling, Storage, and Precautions: storable in a refrigerator for years without any polymerization or decomposition (one of the features that favors the use of this reagent over ethoxyacetylene for many applications).

Carboxylic Anhydrides.

Dehydration of carboxylic acids or dicarboxylic acids to the corresponding anhydrides is effected by using ethoxy(trimethylsilyl)acetylene (1). In general, a carboxylic acid is treated with 1.5 equiv of (1) in CH2Cl2, ClCH2CH2Cl, or MeCN at rt to 60 °C for 2 h to 1 d followed by concentration of the reaction mixture to give a pure anhydride in an almost quantitative yield (eq 1).1 The only byproduct of this reaction is the neutral and volatile ethyl (trimethylsilyl)acetate. Use of ethoxyacetylene for this purpose has been limited because of its instability to heat, high volatility, and low reactivity with some carboxylic acids.6 The reagent (1) resolves these problems and is especially effective for preparation of the carboxylic anhydrides with acid-sensitive functional groups such as (2)1 and (3).7 Suitably functionalized homophthalic anhydrides (2) and (4)8 and their heteroaromatic derivatives (5)9 are key intermediates for total synthesis of natural anthracyclines and their heteroaromatic analogs.

Dehydrative Condensation of Carboxylic Acids with Amines and Alcohols.

In the presence of a mercuric catalyst, (1) causes dehydrative condensation of carboxylic acids with H-acidic materials such as amines and alcohols to give the corresponding amides, esters, lactones, and peptides in high yields.2

Preparation of (Trimethylsilyl)ketene.

Heating of (1) at 120 °C is a convenient method for preparation of Trimethylsilylketene (6) (eq 2).3 This ketene is an easy-handling, storable, and distillable monomeric liquid, and is useful for acylation of sterically hindered alcohols and amines (eq 3). Other useful applications of (6) are represented in the preparation of a-silyl acetates,10 a-silyl ketones,11 a,b-unsaturated esters,12 and silylallenes.17

Cycloaddition Reactions.

Dichloroketene, N-sulfonylimines, Diazomethane, and aroylketenes add to (1) to provide good yields of a cyclobutenone,4 2-azetines,13 a pyrazole,14 and 4-pyrones,15 respectively. Cooligomerization of three molecules of (1) with one molecule of Carbon Dioxide proceeds in the presence of Ni0 catalyst, giving a 2-pyrone derivative in 90% yield.16

1. Kita, Y.; Akai, S.; Ajimura, N.; Yoshigi, M.; Tsugoshi, T.; Yasuda, H.; Tamura, Y. JOC 1986, 51, 4150.
2. Kita, Y.; Akai, S.; Yamamoto, M.; Taniguchi, M.; Tamura, Y. S 1989, 334.
3. Ruden, R. A. JOC 1974, 39, 3607.
4. Danheiser, R. L.; Sard, H. TL 1983, 24, 23.
5. Shchukovskaya, L. L.; Pal'chik, R. I. IZV 1964, 2228.
6. Eglinton, G.; Jones, E. R. H.; Shaw, B. L.; Whiting, M. C. JCS 1954, 1860.
7. Kita, Y.; Okunaka, R.; Honda, T.; Shindo, M.; Taniguchi, M.; Kondo, M.; Sasho, M. JOC 1991, 56, 119.
8. Tamura, Y.; Sasho, M.; Ohe, H.; Akai, S.; Kita, Y. TL 1985, 26, 1549. Tamura, Y.; Akai, S.; Kishimoto, H.; Kirihara, M.; Sasho, M.; Kita, Y. TL 1987, 28, 4583.
9. Kita, Y.; Kirihara, M.; Sekihachi, J.; Okunaka, R.; Sasho, M.; Mohri, S.; Honda, T.; Akai, S.; Tamura, Y.; Shimooka, K. CPB 1990, 38, 1836.
10. Kita, Y.; Sekihachi, J.; Hayashi, Y.; Da, Y.-Z.; Yamamoto, M.; Akai, S. JOC 1990, 55, 1108.
11. Kita, Y.; Matsuda, S.; Kitagaki, S.; Tsuzuki, Y.; Akai, S. SL 1991, 401.
12. Akai, S.; Tsuzuki, Y.; Matsuda, S.; Kitagaki, S.; Kita, Y. JCS(P1) 1992, 2813.
13. Zaitseva, G. S.; Novikova, O. P.; Livantsova, L. I.; Petrosyan, V. S.; Baukov, Yu. I. ZOB 1991, 61, 1389.
14. Kostyuk, A. S.; Knyaz'kov, K. A.; Ponomarev, S. V.; Lutsenko, I. F. ZOB 1985, 55, 2088.
15. Kolesnikova, O. N.; Livantsova, L. I.; Shurov, S. N.; Zaitseva, G. S.; Andreichikov, Yu. S. ZOB 1990, 60, 467.
16. Tsuda, T.; Hasegawa, N.; Saegusa, T. CC 1990, 945.
17. Kita, Y.; Tsuzuki, Y.; Kitagaki, S.; Akai, S. CPB 1994, 42, 233.

Yasuyuki Kita

Osaka University, Japan

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