Ferf-Butyldimethylsilyl group

Reactions of various l-(l,2-propadienyl)cyclopropanols having a substituent at the 1- or 3-position of the propadienyl moiety 55 proceed smoothly at between 0°C and room temperature with 1.1 mole amounts of Co2(CO)8 in either THF or ethyl acetate, and various 2-monosubstituted or 2,3-disubstituted 1,4-hydro-quinone derivatives 58 are obtained in good yields (Scheme 25). In particular, 1-(1,2-propadienyI)cycIopropanoI having the ferf-butyldimethylsilyl group at the 1-position of the 1,2-prop adienyl moiety gives a high yield of the silylated hydroquinone. 

Aldol group transfer polymerization of ferf-butyldimethylsilyl vinyl ether [62] was initiated by pendant aldehyde functions incorporated along a poly(methyl methacrylate) (PMMA) backbone [63]. This backbone was a random copolymer prepared by group transfer polymerization of methyl methacrylate (MMA) and acetal protected 5-methacryloxy valeraldehyde. After deprotection of the aldehyde initiating group, polymerization proceeded by activation with zinc halide in THF at room temperature. The reaction led to a graft copolymer with PMMA backbone and poly(silyl vinyl ether) or, upon hydrolysis of the ferf-butyldimethylsilyl groups, poly(vinyl alcohol) branches. 

In order to check the applicability of the oxathiaphospholane method for the stereocontrolled synthesis of oligo(ribonucleoside 3, 5 -phosphorothioate)s, appropriate oxathiaphospholane monomers possessing 2 -hydroxyl function protected with ferf-butyldimethylsilyl group (40 a-d) were synthesized and sepa-... 

Studies involving 14a and its derivatives were scarce for the next 40 years. In an attempt to prepare [Sjannulene derivative 15a, Youngs and coworkers discovered a Pd-catalyzed route to dibenzopentalenes (Scheme 2.8) [37]. Under standard Sonogashira conditions, 14b was obtained in 67% yield with the desired cyclodimer 15a in only 10% yield. The unexpected dibenzopentalene 14b was presumed to arise from an intramolecular cyclization and subsequent hydrogen atom abstraction from the solvent. The lack of trimer and tetramer in the reaction mixture was most Hkely due to the steric bulk of the flanking ferf-butyldimethylsilyl groups. 

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 asymmetric syntheses, the bulky (i-Pr)3Si group can direct 1,2-addition of phosphite 92 to (S j-triisopropylsilyloxy lactaldehyde (93) to afford adduct 94 preferentially along with the by-product 95 (equation 42)157. The stereochemical outcome results from the bulk of the (i-Pr)3Si protecting group9. Furthermore, the steric congestion in allylic cyanohydrin trimethylsilyl and ferf-butyldimethylsilyl ethers influences their regioselective 1,2- and 1,4-additions to carbonyl compounds under basic conditions158. 

FIGURE 10.1 Some monosaccharide building blocks used in the assembly of (a) HA, (b) CS, and (c) heparin/HS showing the array of protecting groups. All, allyl Bn, benzyl Bz, benzoyl Fmoc, 9-fluorenylmethoxycarbonyl Lev, levulinyl NAP, 2-naphthylmethyl PBB, p-bromobenzyl Phth, phthaloyl PMB, / -methoxybenzyl PMP, p-methoxyphenyl TBDPS, ferf-butyldiphenylsilyl TBS, ferf-butyldimethylsilyl TCA, trichloroacetyl TDS, dimethylthexylsilyl Tol, 4-tolyl. 

On the other hand, in the Polonovski reaction of A-oxides using SKA, carbon-carbon bond-forming product was selectively obtained even if the substrate was allowed to react with ferf-butyldimethylsilyl ketene acetal in acetonitrile.28 It has become apparent that the choice of silyl moiety in SKA influences the course of the reaction. Specifically, in the case of SKA bearing a tert-butyldimethylsilyl group, a (methoxycarbonyl) methyl adduct was preferentially converted to a cyanomethyl adduct, whereas in the case of SKA bearing an O-fert-butyldiphenyl-... 

Cycloaddition of orf/io-quinone 162 with ferf-butyldimethylsilyl ether of sinapyl alcohol (163) yielded the 1,4-dioxane-linked adduct 164, as shown in Scheme 10b, but no regioisomer was detected. The ketal group in 164 was removed under acidic conditions and the derived ketone, a trans-cis mixmre in the ratio of 2 1, on treatment with alkali, yielded the frans-isomer, 165, in a good yield. The ketone 165 was converted to the key intermediate aldehyde 166 through the iodoform reaction, esterification, LAH reduction, and oxidation with Dess-Martin periodinane after protection of the hydroxy groups by MOM groups (Scheme 10b). 

In some cases it may be desirable to block a particular functional group so as to direct lanthanide association to another site. A comparison of the effect of blocking binding at hydroxyl groups by preparing trifiuoroacetate, ferf-butyldimethylsilyl ether and trimethyl silyl ether derivatives was reported. The ferf-butyldimethylsilyl ether derivative was most effective at blocking lanthanide association. 

Recently, Nakamura et al. successfully synthesized a regioisomer of kealiiquinone (Scheme 11) [50]. l-Methyl-2-phenylthio-lff-imidazole 44 was first converted into the 5-substituted imidazole 45, then the benzylic hydroxyl group in 45 was protected by a ferf-butyldimethylsilyl (TBDMS) group, and bromination with N-bromosuccinimide gave the bromide 46. Lithiation by ferf-butyllithium at the 4-position of 46 followed by trapping with 3,4-dimethoxy-2-(methoxymethoxy)benzaldehyde gave the tetrasubstituted imidazole 47 as a diastereomeric mixture. Acetylation of the hydroxy group of 47... 

The answer is to protect the hydroxyl group with a group resistant to base, and the group You met imidazole on p. 178. chosen here was a silyl ether. Such ethers are made by reacting the alcohol with a trialkylsilyl chloride (here ferf-butyldimethylsilyl chloride, or TBDMSCl) in the presence of a weak base, usually imidazole, which also acts as a nucleophilic catalyst (Chapter 12). 

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