Methylketene Bis(trimethylsilyl) Acetal

[31469-22-4]  · C9H22O2Si2  · Methylketene Bis(trimethylsilyl) Acetal  · (MW 218.44)

(reactive nucleophile in Mukaiyama-type aldol reactions;1,2 additions to imines7 and enones;8 alkylations with a-halo sulfides;9 a-hydroxylations10)

Alternate Name: 1,1-bis(trimethylsilyloxy)propene.

Physical Data: bp 63-68 °C/12 mmHg.

Solubility: highly sol organic solvents.

Preparative Methods: ketene bis(trialkylsilyl) acetals are prepared by silylation of lithium trialkylsilyl carboxylates or treatment of the dianions of carboxylic acids with Chlorotrimethylsilane at -78 °C (eq 1).3 Alternatively, silyl carboxylates are silylated by trialkylsilyl triflates in the presence of Triethylamine.4

Handling, Storage, and Precautions: easily hydrolyzed and oxidized by exposure to air. Storage possible in sealed tubes at rt.

Additions to Aldehydes.

Dubois and co-workers examined the stereochemistry of the Lewis acid-catalyzed Mukaiyama aldol condensation of ketene bis(trimethylsilyl) acetals.5 Mainly the anti-hydroxy acid is obtained from methylketene bis(trimethylsilyl) acetal, benzaldehyde, and Titanium(IV) Chloride (eq 2). With increasing size of the alkyl substituent on the ketene, the syn isomer predominates. Fluoride anion also serves as a catalyst, providing predominantly syn product (eq 2).6

Additions to Imines.

A diastereoselective synthesis of b-amino esters by TiCl4-mediated reaction of N-tosylaldimines with ketene bis(trimethylsilyl) acetals was realized (eq 3).7

Alkylation by a-Halo Sulfides.

The Zinc Bromide-catalyzed phenylthioalkylation of methylketene bis(trimethylsilyl) acetal with a-chloro sulfides provides phenylthiolactones which can be converted to a,b-unsaturated g- and d-lactones (eq 4).9

Additions to a,b-Unsaturated Carbonyl Compounds.

The regio- and stereoselectivity of TiCl4-catalyzed 1,2- and 1,4-additions of ketene bis(trimethylsilyl) acetals to a,b-unsaturated enones and enals were investigated by Bellassoued and Mladenova.8


Treatment with peroxy acids in hexane followed by acidic workup allows isolation of a-hydroxy acids in good yields.10 Bissilyl ketene acetals devoid of b-protons undergo a clean sigmatropic ene reaction with 1O2 to generate the a-silylperoxy silyl ester quantitatively (eq 5).11

Related Reagents.

1,2-Diethoxy-1,2-bis(trimethylsilyloxy)ethylene; Ketene Bis(trimethylsilyl) Acetal; Ketene Diethyl Acetal; 1-Methoxy-2-methyl-1-(trimethylsilyloxy)propene; 1-Methoxy-1-(trimethylsilyloxy)propene; 1-Methoxy-2-trimethylsilyl-1-(trimethylsilyloxy)ethylene; Methylketene Dimethyl Acetal; Tetramethoxyethylene; Tris(trimethylsilyloxy)ethylene.

1. Mukaiyama, T. OR 1982, 28, 203.
2. Mukaiyama, T.; Murakami, M. S 1987, 1043.
3. Ainsworth, C.; Kuo, Y.-N. JOM 1972, 46, 73.
4. Emde, H.; Simchen, G. LA 1983, 816.
5. Dubois, J.-E.; Axiotis, G.; Bertounesque, E. TL 1984, 25, 4655.
6. (a) Bellassoued, M.; Dubois, J.-E.; Bertounesque, E. TL 1986, 27, 2623. (b) Nakamura, E.; Yamago, S.; Machii, D.; Kuwajima, I. TL 1988, 29, 2207.
7. Shimada, S.; Saigo, K.; Abe, M.; Sudo, A.; Hasegawa, M. CL 1992, 1445.
8. Bellassoued, M.; Mladenova, M. PS 1991, 60, 295.
9. Khan, H. A.; Paterson, I. TL 1982, 23, 5083.
10. Rubottom, G. M.; Marrero, R. JOC 1975, 40, 3783.
11. Adam, W.; Alzérreca, A.; Liu, J-C.; Yany, F. JACS 1977, 99, 5768.

Peter Wipf

University of Pittsburgh, PA, USA

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