(1; M = K)

[53127-82-5]  · C4H11KSi  · Trimethylsilylmethylpotassium  · (MW 126.34) (2; M = Na)

[53127-81-4]  · C4H11NaSi  · Trimethylsilylmethylsodium  · (MW 110.23)

(can act as a strong base with benzylic and allylic compounds2)

Preparative Methods: trimethylsilylmethylpotassium (1) and -sodium (2) are prepared by reaction of Bis(trimethylsilyl)mercury with the appropriate metal as a suspension in cyclohexane.2,3 Trimethylsilylmethylsodium can also be prepared by reaction of Bis(trimethylsilyl)methane with Sodium Methoxide in HMPA.4

Handling, Storage, and Precautions: both of these organometallic reagents should be prepared just prior to use and not stored for extended periods. All reactions with these reagents should be performed under an inert atmosphere.

Base Reactions.

Both metal reagents (1) and (2) act as bases. The tricyclic ether (3) is readily deprotonated by the hindered base (1), but pentylsodium or butylpotassium proved superior in other cases.2 However, reagent (1) provides an alternative to the n-Butyllithium-Potassium t-Butoxide system (eq 1).1

Both reagents (1) and (2) react with benzylic compounds to afford benzyl anions. The reaction can accommodate alkyl or silyl groups on the benzylic position or as substituents on the aromatic ring (eq 2).2,3

The use of trimethylsilylmethylpotassium (1) as a base also allows deprotonation of allylic positions. The allyl carbanions produced by the action of substrate with (1) react with Ethylene Oxide to afford the 4-en-1-ol product; unsymmetrical allylic anions can result in a mixture of products, although reaction is favored at the least substituted center (eq 3).5

The potassium reagent (1) will deprotonate simple alkenes to give allylic anions.2 Subsequent reaction with a chloroborane results in the allylic borane, which, in turn, can be converted to an allyl alcohol (eq 4).6

Pentadienyl-type organometallic reagents are available by reaction of (1) with homoconjugated and conjugated dienes, without significant polymerization. The regioselectivity of the metalation is dependent on the structure of the substrate, U-shaped delocalized systems usually being preferred.7 However, the factors affecting the regioselectivity are subtle, as illustrated by reaction at the 14-position of 7-dehydrocholesterol (4) (eq 5).8

Peterson Alkenation.

Trimethylsilylmethylsodium (2) is prepared in situ by the action of sodium methoxide on bis(trimethylsilyl)methane (5),4 and reacts with nonenolizable carbonyl compounds to provide alkenes by a Peterson alkenation reaction (eq 6). Alternative procedures are available that circumvent the use of HMPA, and allow reaction with enolizable carbonyl compounds.9

Related Reagents.

Trimethylsilylmethyllithium; Trimethylsilylmethylmagnesium Chloride.

1. Schlosser, M. AG(E) 1974, 13, 701.
2. Hartmann, J.; Schlosser, M. HCA 1976, 59, 453.
3. Hart, A. J.; O'Brien, D. H.; Russell, C. R. JOM 1974, 72, C19.
4. Sakurai, H.; Nishiwaki, K.-i.; Kira, M. TL 1973, 4193.
5. Hartmann, J.; Schlosser, M. S 1975, 328.
6. Zaidlewicz, M. JOM 1985, 293, 139.
7. (a) Schlosser, M.; Rauchschwalbe, G. JACS 1978, 100, 3258. (b) Bosshardt, H.; Schlosser, M. HCA 1980, 63, 2393. (c) Schlosser, M.; Bosshardt, H.; Walde, A.; Stähle, M. AG(E) 1980, 19, 303.
8. Moret, E.; Schlosser, M. TL 1984, 25, 1449.
9. (a) Ager, D. J. OR 1990, 38, 1. (b) Johnson, C. R.; Tait, B. D. JOC 1987, 52, 281.

David J. Ager

The NutraSweet Company, Mount Prospect, IL, USA

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