Silyl protecting groups triisopropyl

Pyrroles and indoles can be protected with the r-butyldimethylsilyl group by treatment with TBDMSC1 and n-BuLi or NaH.31 Triisopropyl silyl chloride (NaH, DMF, 0°-rt, 73% yield) has been used to protect the pyrrole nitrogen in order to direct electrophilic attack to the 3-position.32 It has also been used to protect an indole.33 This derivative can be prepared from the silyl chloride and K.34 The silyl protective group is cleaved with Bu4N+F , THF, rt or with CF3COOH. 

The 0-silylation reaction of alcohols is important as a protection method of hydroxyl groups. 0-Silylations of liquid or crystalline alcohols with liquid or crystalline silyl chlorides were found to be possible in the solid state. For example, when a mixture of powdered L-menthol (26), ferf-butyldimethylsilyl chloride (27), and imidazole (28) was kept at 60 °C for 5 h, 0-tert-butyldi-methylsilyl L-menthol (29) was obtained in 97% yield [8] (Scheme 4). Similar treatments of 26 with the liquid silyl chlorides, trimethyl- (30a) and triethylsilyl chloride (30b), gave the corresponding 0-silylation products 31a (89%) and 31b (89%), respectively, in the yields indicated [8] (Scheme 4). However, 0-silylation of triisopropyl- (30c) and triphenylsilyl chloride (30d) proceeded with difficultly even at 120 °C and gave 31c (57%) and 31d (70%), respectively, in relatively low yields. Nevertheless, when the solvent-free silylation reactions at 120 °C were carried out using two equivalents of 30c and 30d, 31c (77%) and 31d (99%) were obtained, respectively, in relatively high yields. 

In the presence of even only mild electrophiles, cycloproparenes react via cleavage of the cyclopropane ring. However, the extremely bulky bis(triisopropyl-silyl) group offers efficient steric protection, and 302 is unreactive towards Br2. It reacts however with 67% HNO at 25 °C to afford the 3-nitro derivative 303 in 58% yield. The nitro group of 303 has been reduced to the amine which was acetylated. Reaction of 303 with LiAlH, in turn, afforded the corresponding azo compound. ... 

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