Silyl groups, deprotection, tetrabutylammonium fluoride

Deprotection of Silyl Groups. Tetrabutylammonium fluoride has been used widely as a reagent for the efficient cleav-... 

Silyl ethers are widely used protective groups because they also have a convenient method of deprotection treatment with tetrabutylammonium fluoride (n-Bu4NF or TBAF, pronounced t-baff ).The reaction of an alcohol (ROH) with trimethylsUyl chloride (Me sSiCl or TMSCl) and base makes the protected trimethylsilyl ether (ROTMS). Variation of the alkyl groups on the silicon (e.g., triisopropylsUyl TIPS, or r-butyldimethylsilyl TBDMS/TBS) increases the silyl ether s stability, especially toward acidic conditions, and also allows for selective protection of less hindered alcohols. 

Several methods can be used for deprotection of silyl groups under acidic or basic conditions [27]. Under basic conditions, Oscarson et al. [5] converted 37a into 1 (61%) with tetrabutylammonium bromide and potassium fluoride under the action of microwave irradiation at 180 °C for 2 min. Under slightly acidic conditions, they used montmorillonite KIO clay in methanol-water (1 1) at 150 °C for 4 min and 3 min, to obtain 3 in high yields (85% and 91%, respectively) (Scheme 12.20). Under... 

The 6-mono-0-trityl cellulose or the more efficient 6-0-mono-0-(4-monomethyoxytrityl) derivative, and 6-mono-O-TDS cellulose were used to synthesize regioselectively functionalized cellulose ethers at positions 2 and 3 after the exclusive cleavage of the protecting groups (Table 16.10). In case of the trityl derivatives, the deprotection is carried out most efficiently with HCl in a suitable solvent. For TDS protected derivatives, tetrabutylammonium fluoride in THF is most successful for the cleavage of the silyl groups. 

Xerulinic acid (151) inhibited the biosynthesis of cholesterol in HeLa S3 cells by blocking HMG-CoA synthase. Bisstannane 147 was transmetallated to the zincate intermediate and was Negishi cross-coupled with butenolide 148 to give the all tra 5-polyene 149. The Stille reaction of 149 with enediyne 150 followed by deprotection of the silyl group with tetrabutylammonium fluoride afforded xerulinic acid (151). 

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