[5180-98-8] · C7H20OSi2 · (Methoxydimethylsilyl)(trimethylsilyl)methane · (MW 176.45)
(Peterson alkenation reagent; synthesis of vinyl silanes from aldehydes and ketones1)
Solubility: sol common organic solvents (THF, Et2O, CH2Cl2, pentane, etc.)
Analysis of Reagent Purity: 1H NMR (CDCl3) d 3.38 (s, 3 H), 0.10 (s, 6 H), 0.02 (s, 9 H), -0.14 (s, 2 H); 13C NMR (CDCl3) d 49.94, 4.14, 1.13, 0.03.3
Preparative Methods: prepared in 75% yield by treatment of MeOSiMe3 with t-Butyllithium in pentane at -78 °C to ambient temperature followed by addition of Chlorotrimethylsilane at 0 °C.2 Alternatively, the reagent is prepared in 34% yield by treatment of Trimethylsilylmethylmagnesium Chloride with Dichlorodimethylsilane followed by LiOMe in THF.3
Handling, Storage, and Precautions: use in a well-ventilated fume hood. Contact with the eyes and skin should be avoided.
The synthesis of vinylsilanes via alkenation reactions of [bis(trimethylsilyl)methyl]lithium is restricted to nonenolizable aldehydes and ketones.5 However, [(methoxydimethylsilyl)(trimethylsilyl)methyl]lithium (1), generated from the title reagent by treatment with t-Butyllithium in pentane at rt, undergoes Peterson alkenation with aldehydes and ketones to give vinylsilanes in good yield (eq 1). Interestingly, the methoxydimethylsilyl unit is preferentially eliminated from the b-hydroxydisilane intermediate. Alkenation reactions of (1) with aldehydes and unsymmetrical ketones are only moderately stereoselective (eqs 2 and 3).
Avery and co-workers have applied this methodology to the synthesis of vinylsilane intermediates utilized in syntheses of artemisinin analogs (eqs 4 and 5).6 The low efficiency of these Peterson alkenation reactions (31-50%) suggests that the relatively hindered carbonyl groups undergo competitive deprotonation by the anion (1).
William R. Roush
Indiana University, Bloomington, IN, USA