Triethylsilyl TES Ethers

The ratio of pleasure to pain is quite favourable with TES ethers. Like the TMS group, the TES group is easy to introduce and easy to remove in the presence of other silyl protecting groups but it is also sufficiently stable to endure column chromatography and it is resistant to many oxidation, reduction, and organometaliic reactions. 

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A step from a synthesis of Phorboxazole B illustrates that mildly basic conditions, sodium hydrogen carbonate in methanol at room temperature, will also selectively cleave a primary TMS ether in the presence of a primary triethylsilyl (TES) ether [Scheme 4.4J.7... 

Condensation of 37 with the JK-ring carboxylic acid 38 under the Yam-aguchi conditions provided ester 39 in high yield (Scheme 4). After selective removal of the triethylsilyl (TES) ether, the resultant alcohol was converted to the allylstannane by the standard procedure. DIBALH reduction of the ester followed by in situ esterification with chloroacetic anhydride/DMAP/pyridine delivered of-chloroacetoxy ether 40. Intramolecular cyclization of 40 with magnesium bromide etherate in acetonitrile afforded the desired product 41 as a single stereoisomer in 82% yield. RCM reaction of 41 using 18 pro-... 

The triethylsilyl ether is approximately 10-100 times more stable than the TMS ether and thus shows a greater stability to many reagents. Although TMS ethers can be cleaved in the presence of TES ethers, steric factors will play an important role in determining selectivity. The TES ether can be cleaved in the presence of a /-butyldimethylsilyl ether using 2% HE in acetonitrile. In general, methods used to cleave the TBDMS ether are effective for cleavage of the TES ether. 

Silyl ethers, such as TMS, triethylsilyl (TES), triisopropylsilyl (TIPS), lerl-butyldi-methylsilyl (TBS), and terl-butyldiphenylsilyl (TBDPS) ethers (Scheme 2.6), are frequently used in carbohydrate chemistry due to their unique reactivity and steric effect (see Section 2.4.1) [1, 2], These groups are typically introduced onto the molecule by treatment with the corresponding silyl halide or triflate (OTf) and a base, such as Et3N, pyridine, 2,6-lutidine, or imidazole. 

Three of the most common procedures for the formation TES ethers have been selected for their large scale preparative value. Triethylsilyl ethers are prepared by the reaction of the alcohol with chlorotriethylsilane in the presence of a catalytic amount of imidazole [Scheme 4.23]30 or DMAP31 Triethylsilyl triflate in the presence of pyridine [Scheme 4.24]32 or 2,6-lutidine [Scheme 4.25]23 can be... 

Triethylsilyl triflate. This has become a popular reagent for the preparation of TES ethers. Commonly used bases are pyridine and 2,6-lutidine. The most frequently used solvent is CH2CI2, but others such as CH3CN have also been used. 

In the second step, the resulting alcohol is protected as triethylsilyl ether (TES). 

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