Silyl protecting groups stability

The resulting molecule bears a primary and a secondary alcohol function. The primary alcohol can be selectively protected by using TBSC1. This silyl protecting group provides excellent stability towards base, but is relatively sensitive to acid. Lastly the secondary alcohol is acylated using propionyl chloride in a standard procedure to give ester 8. 

The most stable common silyl protecting group (triisopropylsilyl or TIPS) has three branched alkyl substituents to protect the central silicon from attack by nucleophiles which would lead to cleavage. All three hindered silyl groups (TBDMS, TBDPS, and TIPS) have excellent stability but can still be removed with fluoride. 

Silyl protecting groups other than TMS and TBDMS are usually applied only if a modified acid stability is wanted. Thus, the triethylsilyl (TES) group shows a sensitivity to hydrolysis and nucleophilic attack intermediate between the TMS and the TBDMS groups. The triisopropylsilyl (TIPS), ° the r-bu-tyldiphenylsilyl (TBDPS) and the thexyldimethylsilyl (TDS) groups are considerably more stable... 

Carboxylic Acid Protection. - Increasing the bulk of the substituents generally increases the stability of silyl protecting groups. This has been taken a step further with the introduction of the... 

Silyl groups have found broad appeal as protective groups because their reactivity and stability can be tailored by varying the nature of the substituents on the silicon. Their ability to migrate from one hydroxyl to another is a property that can be used to advantage, but more often, it is a nuisance. The migratory apti-... 

Silyl Ethers as Protective Groups for Alcohols. Oxidative Deprotection and Stability Under Alcohol Oxidation Conditions, Muzart. J. Synthesis. 1993, 11... 

Oxidative addition of a silyl-protected 4-(bromomethyl)phenol precursor to (tme-da)Pd(II)Me2 (tmeda = tetramethylethylenediamine), followed by ethane reductive elimination, resulted in formation of the benzylic complex 16 (Scheme 3.10). Exchange of tmeda for a diphosphine ligand (which is better suited for stabilizing the ultimate Pd(0) QM complex), followed by removal of the protecting silyl group with fluoride anion, resulted in the expected p-QM Pd(0) complex, 17, via intermediacy of the zwitterionic Pd(II) benzyl complex. In this way a stable complex of p-BHT-QM, 17b, the very important metabolite of the widely used food antioxidant BHT20 (BHT = butylated hydroxytoluene) was prepared. Similarly, a Pd(0) complex of the elusive, simplest /)-QM, 17a, was obtained (Scheme 3.10). 

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