Desilylation with TBAF

Enones and enoates undergo 1,2-reduction [115, 191]. Lipshutz et al. reported the effective protection of carbonyl functions by the triisopropylsilyl acyl silane group (TIPS), which allowed the selective conversion of alkenes or alkynes to the corresponding zirconocene complexes [24]. The aldehyde could subsequently be regenerated by desilylation with TBAF [186]. 

The major isomer 34 is desilylated with TBAF, and oxidative cleavage of the diol with sodium periodate generates the corresponding aldehyde 35, the racemic form of which is a known intermediate in the total synthesis of racemic CP compounds. The conversion to the indoline derivative mt-31 therefore follows the strategy of the racemic route. Circular dichroism (CD) spectroscopy verified the identity of the synthetic mt-31 as the enantiomer of the naturally derived indoline (—)-31. Synthetic ent-31 was also processed to give ent-1 and ent-2. 

Diphenyl silaketals 196 can be readily converted to the ( -symmetrical 1,4-diol 293 by reduction with Raney-Ni, followed by desilylation with TBAF in 65% yield. Another potentially powerful application of cyclic alkoxysilanes 196 consists in dihydroxylation with catalytic amount of osmium tetraoxide in the presence of A-methylmorpholine A-oxide (NMO), followed by treatment with TBAF which gives D-altriol 294 (Scheme 51) <1998JOC6768>. 

Surprisingly, Lewis acids are seldom applied to the deprotection of TBS ethers even though in certain circumstances they have advantages. A case in point is the transformation depicted in Scheme 4,39.5S The hydrolytic lability of the ox-alimide function in 39.1 precluded desilylation with TBAF or methanolic acid but trifluoroborane etherate in acetonitrile59 at 0 °C rapidly and cleanly accomplished the desired desilylation to give the diol 39,2 in 93% yield. 

The yields after desilylation with TBAF in THF or K2CO3 in MeOFI... 

On the other hand, catalytic hydrogenation of 121 followed by protection of the resulting amine with p-methoxybenzyl S-(4,6-dimethylpyrimidin-2-yl)thiocarbonate afforded the carbamate 124, which underwent desilylation with TBAF followed by Swem oxidation of the resulting primary hydroxyl group to provide the aldehyde 125. Removal of the protecting groups from 125 with aqueous sulfurous acid at room temperature provided... 

The iV-dicyanomethylids of pyridazine, and especially of phthalazine, undergo 1,3-dipolar cycloaddition with bis(trimethylsilyl)acetylene to give fused pyrrole derivatives (Scheme 40) which can be quantitatively desilylated with TBAF <83H(20)1009>. 

The corresponding compounds 48 were obtained in 73 78% yields by the standard method in optically pure form. The compound with R = Si(z-Pr)3 could be easily desilylated with TBAF to furnish 49, which was methylated to afford 50. 

Trimethylsilyloxyfuran 338 has shown promise as a masked butenolide fragment To fuUy exploit these qualities, the threo versus erythro (339 vs 340) diastereoselectivity in aldol-type additions has to be controlled. In fact it has been shown that this is easily achieved by appropriate reaction conditions. Applying Mukaiyama conditions (i.e., using the silyl enol ether as the donor in the presence of a Lewis acid such as TESOTf to generate oxonium species) leads to threo preference for 339, presumably via an open transition state, whereas desilylation with TBAF generates the erythro-diastereomer 340, this time via a closed Diels-Alder (or Zimmerman-Traxler)-like transition state. In both cases, chelating effects can be ruled out... 

However, in this case the electron-rich 1-methoxypropyne was used as the monoalkyne. First, 108 was converted into yne-ynamide 109 by three steps, including a Sonogashira reaction with trimethylsilylacetylene and the ynamide formation based on the alkynyliodonium salt 105. Yne-ynamide 109 was then alkylated with iodopen-tane, and subsequent desilylation with TBAF provided the diyne 110 (44% yield over two steps). The key cyclotrimerization of diyne 110 with 1-methoxypropyne was carried out in toluene at room temperature in the presence of 10 mol % of Wilkinson s catalyst and afforded chemo- and regioselectively carbazole 111 (82% yield, isomer... 

Considering the similarity of the hydroxyl group in alcohols and silanols, Gevorgyan developed a silanol-directed palladium-catalyzed C-H activation/C-O cyclization of phenoxy silanols [61]. The obtained oxasilacycles were further desilylated with TBAF to give catechols. In a follow-up work, the same group disclosed a palladium-catalyzed C-H oxygenation with benzylsilanols to achieve oxasilacycles under similar conditions (Scheme 3.32) [62]. The obtained oxasilacycles proved to be valuable synthetic intermediates and could be converted to a variety of useful compounds. 

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