[91899-54-6]  · C3H9CuSi  · Trimethylsilylcopper  · (MW 136.76)

(nucleophilic silylmetal reagent useful for the regioselective preparation of allyltrimethylsilanes from allylic halides,2-4 allylic sulfonates,4 and allylic phosphates5)

Preparative Method: prepared in situ by adding 1 equiv of Copper(I) Iodide dissolved in dimethyl sulfide (2.5 M solution) to a vigorously stirred solution of 1 equiv of Trimethylsilyllithium6 (prepared from hexamethyldisilane and methyllithium-lithium bromide complex) in HMPA at 0-5 °C under argon.2 The reagent is used immediately in silylation reactions.

Handling, Storage, and Precautions: prepared and used under dry air-free conditions (argon atmosphere, dry solvents, etc.). Since reactions with this reagent employ HMPA (a carcinogen) as solvent, suitable precautions should be taken. Use in a fume hood.

Silylcopper Reagents.1

Trimethylsilylcopper (TMSCu) is one of the many silylcopper reagents which were developed in the 1980s and used in the synthesis of allylsilanes from various allylic substrates. Other well-studied silylcopper reagents include (Me3Si)2CuLi,7 (Me3Si)Cu(CN)Li,8 (PhMe2Si)2CuLi,7,9-11 and (PhMe2Si)2Cu(CN)Li2.12-14 In all cases, these reagents are prepared in situ from 1 equiv of a silyllithium reagent (Me3SiLi or PhMe2SiLi) by reaction with 0.5-1.0 equiv of copper(I) iodide or copper(I) cyanide.

Synthesis of Allylsilanes.

TMSCu reacts with a variety of allylic substrates to form allylsilanes stereoselectively and in good to excellent yields. Thus the reagent reacts readily with primary allylic halides,2-4 sulfonates from secondary and tertiary alcohols,4 and primary and secondary allylic phosphates5 to yield a variety of allylsilanes. Representative examples of these reactions are shown in eqs 1-3. This methodology seems particularly attractive for the synthesis of 3-trimethylsilyl-1-alkenes which are presently unavailable by other methods. For example, (E)-8-t-butyldiphenylsilyloxy-2,6-dimethyl-3-trimethylsilyl-1,6-octadiene, a key intermediate in Corey's synthesis of tricyclohexaprenol, has been prepared from a primary allylic chloride using this methodology (eq 4).15 Moreover, this method has been used in the preparation of 2,3-bis(trimethylsilyl)alk-1-enes (eq 5)4 and (2-Bromoallyl)trimethylsilane (eq 6),2 a useful intermediate in organic synthesis.8

The reactions of TMSCu are in marked contrast to the reactions of Trimethylsilyllithium with similar substrates.3,4 Whereas treatment of a 1-chloro-2-alkene with TMSCu affords a 3-trimethylsilyl-1-alkene, reaction of TMSLi with these same starting materials yields terminal (E)-allylsilanes where the stereochemistry of the double bond is retained in the product (eq 7). Thus a single allylic halide yields either of two regioisomers by proper choice of reaction conditions. With allylic phosphates, TMSCu affords as major product the allylsilane resulting from attack by what is formally an SN2-like reaction. With TMSLi, however, the major product is always the isomeric allylsilane having a more substituted internal double bond (eq 8).

Other silylcuprate reagents have also been used to prepare allylsilanes from allylic halides,10 acetates,11,13 and urethanes.13c,14,16 Moreover, other silylmetal reagents have been used in similar preparations of allylsilanes. For example, silylaluminum reagents have been used to prepare allylsilanes from allylic acetates17 and allylic phosphates,18 and silylmanganese reagents react with allylic sulfides and allylic ethers.19 One advantage that the present methodology has over many other methods is that it utilizes a trimethylsilylmetal reagent to afford an allyltrimethylsilane. The silyl byproducts obtained in the preparation and reaction of these allylsilanes are volatile and easily separable from the desired product. Many of the other existing methods yield allylsilanes where one or more of the alkyl groups on the silicon is replaced by phenyl.

Related Reagents.

Lithium Cyano(dimethylphenylsilyl)cuprate; Trimethylsilyllithium.

1. (a) Sarkar, T. K. S 1990, 969. (b) Colvin, E. W. Silicon Reagents in Organic Synthesis; Academic: New York, 1988; pp 27-29, 51-55. (c) Colvin, E. W. Silicon in Organic Synthesis; Butterworths: Boston, 1981; pp 134-140.
2. Smith, J. G.; Quinn, N. R.; Viswanathan, M. SC 1983, 13, 1.
3. Smith, J. G.; Quinn, N. R.; Viswanathan, M. SC 1983, 13, 773.
4. Smith, J. G.; Drozda, S. E.; Petraglia, S. P.; Quinn, N. R.; Rice, E. M.; Taylor, B. S.; Viswanathan, M. JOC 1984, 49, 4112.
5. Smith, J. G.; Henke, S. L.; Mohler, E. M.; Morgan, L.; Rajan, N. I. SC 1991, 21, 1999.
6. Still, W. C. JOC 1976, 41, 3063.
7. Ager, D. J.; Fleming, I. CC 1978, 177.
8. Trost, B. M.; Chan, D. M. T. JACS 1982, 104, 3733.
9. Ager, D. J.; Fleming, I.; Patel, S. K. JCS(P1) 1981, 2520.
10. (a) Laycock, B.; Maynard, I.; Wickham, G.; Kitching, W. AJC 1988, 41, 693. (b) Laycock, B.; Kitching, W.; Wickham, G. TL 1983, 24, 5785.
11. Fleming, I.; Marchi, D., Jr. S 1981, 560.
12. Fleming, I.; Newton, T. W.; Roessler, F. JCS(P1) 1981, 2527.
13. (a) Fleming, I.; Terrett, N. K. JOM 1984, 264, 99. (b) Fleming, I.; Terrett, N. K. TL 1983, 24, 4151. (c) Fleming, I.; Thomas, A. P. CC 1985, 411.
14. Fleming, I.; Thomas, A. P. CC 1986, 1456.
15. Corey, E. J.; Burk, R. M. TL 1987, 28, 6413.
16. Fleming, I.; Newton, T. W. JCS(P1) 1984, 1805.
17. Trost, B. M.; Yoshida, J.; Lautens, M. JACS 1983, 105, 4494.
18. Okuda, Y.; Sato, M.; Oshima, K.; Nozaki, H. TL 1983, 24, 2015.
19. (a) Fugami, K.; Oshima, K.; Utimoto, K.; Nozaki, H. TL 1986, 27, 2161. (b) Fugami, K.; Hibino, J.; Nakatsukasa, S.; Matsubara, S.; Oshima, K.; Utimoto, K.; Nozaki, H. T 1988, 44, 4277.

Janice Gorzynski Smith

Mount Holyoke College, South Hadley, MA, USA

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