[84645-45-4]  · C4H9LiN2Si  · Diazo(trimethylsilyl)methyllithium  · (MW 120.16)

(nucleophilic diazo species for introduction of one carbon; used in homologation and alkenylation of ketones,2,4,5 preparation of diazo ketones,6 acylsilanes,7 vinylsilanes,8 and heterocycles9,10)

Alternate Names: lithiotrimethylsilyldiazomethane; trimethylsilyldiazomethyllithium.

Solubility: sol THF/hexane mixtures in which it is generated; precipitates out of ether/hexane.

Preparative Method: prepared in situ by lithiation of Trimethylsilyldiazomethane using n-Butyllithium.

Handling, Storage, and Precautions: handle as for other organolithium reagents; stable in solution below 0 °C. Use in a fume hood.

Homologation Reactions of Ketones.

When generated in pentane/THF at -100 °C, diazo(trimethylsilyl)methyllithium reacts with ketones (three examples) and benzaldehyde to give the unstable 1-diazo-1-trimethylsilyl-2-alkanols (eq 1).2 On gentle warming, the diazo alcohols rapidly lose N2 to give trimethylsilyl epoxides. Since such epoxides readily give aldehydes on treatment with acid,3 the method represents an overall homologation of a ketone to the next higher aldehyde.

When diaryl ketones are used, diarylalkynes are formed in good yield (eq 2).4 The reaction presumably proceeds via the diazoalkene followed by aryl migration with loss of nitrogen.

In contrast to the above, a more recent study, using slightly different conditions, reports that whereas aldehydes give terminal alkynes (eq 3), ketones give cyclopentene derivatives, presumably by intramolecular C-H insertion of intermediate alkylidenecarbenes (eq 4).5 No detectable amounts of diazo alcohols or epoxysilanes were produced.

Preparation of Diazo Ketones.

Diazo(trimethylsilyl)methyllithium reacts with lactones to give the product of ring opening, the diazo alcohol, although the silyl group is lost during workup (eq 5).6 The diazo alcohol can subsequently be cyclized to the corresponding oxepane by treatment with Dirhodium(II) Tetraacetate.

Preparation of Acylsilanes.

Diazo(trimethylsilyl)methyllithium is alkylated by a range of alkyl halides RX (R = alkyl, benzyl) to give the corresponding diazosilanes, which are oxidized to the acylsilanes in reasonable yield by treatment with m-Chloroperbenzoic Acid (eq 6).7

Preparation of Vinylsilanes ((E)-Trimethylsilylalkenes).

Treatment of trimethylsilyldiazoalkanes, obtained by alkylation of diazo(trimethylsilyl)methyllithium with RCH2X, with Copper(I) Chloride gives excellent yields of (E)-1-trimethylsilylalkenes (eq 7).8

Preparation of Heterocycles.

On reaction with methyl esters, diazo(trimethylsilyl)methyllithium (2 equiv) gives 2-substituted 5-trimethylsilyltetrazoles in 50-90% yield (eq 8).9a Similarly, reaction with nitriles gives 1,2,3-triazoles in high yield (eq 9).9b Reaction with (Me3Si)2C=PCl leads to 1,2,4-diazaphospholes (eq 10).10

Related Reagents.

Triisopropylsilyldiazomethane can be similarly converted into its lithium derivative.11 Diazo compounds containing tin (R3SnCHN2) and germanium (R3GeCHN2) are also known,1 but have not been used in synthesis. Other lithiated diazo compounds (for example, see Ethyl Diazolithioacetate) are covered elsewhere, as are other lithiated silanes.

1. For a review on organometallic derivatives of diazo compounds, see: Kruglaya, O. A.; Vyazankin, N. S. RCR 1980, 49, 357.
2. Schöllkopf, U.; Scholz, H.-U. S 1976, 271.
3. Stork, G.; Ganem, B. JACS 1973, 95, 6152.
4. Colvin, E. W.; Hamill, B. J. JCS(P1) 1977, 869.
5. Ohira, S.; Okai, K.; Moritani, T. CC 1992, 721.
6. Davies, M. J.; Moody, C. J.; Taylor, R. J. JCS(P1) 1991, 1.
7. Aoyama, T.; Shioiri, T. TL 1986, 27, 2005.
8. Aoyama, T.; Shioiri, T. TL 1988, 29, 6295.
9. (a) Aoyama, T.; Shioiri, T. CPB 1982, 30, 3450. (b) Aoyama, T.; Shioiri, T. CPB 1982, 30, 3849.
10. Schnurr, W.; Regitz, M. S 1989, 511.
11. Arthur, M. P.; Goodwin, H. P.; Baceiredo, A.; Dillon, K. B.; Bertrand, G. OM 1991, 10, 3205.

Christopher J. Moody

Loughborough University of Technology, UK

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