Trimethylsilylketene

Abstract

[4071-85-6] C5H10OSi (MW 114.24) (reactive acylating agent for amines and alcohols;2 building block for synthesis of coumarins;3 synthesis of α-silyl ketones via the addition of organocerium reagents;4 treatment with stabilized ylides forms trimethylsilyl-substituted allenes;2a cycloaddition with aldehydes affords β-lactones;5 forms small rings with diazomethane;6 treatment with n-BuLi forms a ketene enolate7) Physical Data: 2a,7 bp 81–82 °C; d 0.80 g cm−3. Solubility: sol CH2Cl2, CHCl3, CCl4, THF, diethyl ether, and most standard organic solvents; reacts with alcoholic and amine solvents. Form Supplied in: colorless oil; not commercially available. Analysis of Reagent Purity: 8 IR (CCl4) 2130 cm−1; 1H NMR (60 MHz, CCl4) δ 1.65 (s, 1 H), 0.12 (s, 9 H) ppm; 13C NMR (50.3 MHz, CDCl3) δ 179.4, 0.5, −0.2 ppm. Preparative Method: most often prepared (eq 1) by pyrolysis of Ethoxy(trimethylsilyl)acetylene at 120 °C (100 mmol scale, 65% yield).2a Recently, pyrolysis of t-butoxy(trimethylsilyl)acetylene has been shown to be a convenient alternative for the preparation of trimethylsilylketene 1. Thermal decomposition of t-butoxy(trimethylsilyl)acetylene causes elimination of 2-methylpropene slowly at temperatures as low as 50 °C and instantaneously at 100–110 °C (30 mmol scale, 63% yield).8 The main advantage of this method is that it is possible to generate trimethylsilylketene in the presence of nucleophiles, leading to in situ trimethylsilylacetylation (eq 2). Increased shielding of the triple bond prevents problems such as polymerization and nucleophilic attack that occur when the ketene is generated in situ from (trimethylsilyl)ethoxyacetylene. Trimethylsilylketene can also be prepared (eq 3) via the dehydration of commercially available Trimethylsilylacetic Acid with 1,3‐Dicyclohexylcarbodiimide (DCC) in the presence of a catalytic amount of Triethylamine (100 mmol scale, 63%).9 Other typical methods used for ketene generation such as dehydrohalogenation of the acyl chloride10 and pyrolysis of the anhydride10b,11 have been applied to the preparation of 1; however, both methods afford low yields. (1) (2) (3) Purification: purified by distillation at 82 °C/760 mmHg. Handling, Storage, and Precautions: unusually stable for an aldoketene with respect to dimerization and decomposition. Samples stored neat under nitrogen at room temperature show no noticeable decomposition after several months.