Triethylsilyl group

The molecular weight (M 10,200,000) represents the highest molecular weight known to date for a linear, synthetic copolymer. DFT calculations suggest that steric congestion, derived from the triethylsilyl group and the amine moiety, near the polymerization reaction center diminishes the rates of chain termination or transfer processes yet permits the monomer access to the active site and the monomer s insertion into the metal-carbon bond (Fig. 21). 

MCM-41 has been employed as an acidic solid support for deprotection of the triethylsilyl group A. Itoh, T. Kodama,... 

Sometimes the triethylsilyl grouping is more suitable for poly-acetylene synthesis because of its greater stability, namely in the Cadiot-Chodkiewicz coupling reaction44 of a halogenoacetylene with unprotected l-phenyl-buta-l,3-diyne (39)... 

An unusual enolate of the 3-triethylsilyl-pro-tected 1,3,5-tricarbonyl compound 69 was applied to aldehyde 70 by Danishefsky et al., forming aldol 71 in 74 % yield and with a 5.5 1.0 ratio - remarkable considering that in this case no double stereodifferentiation improves the induction [10, 52J. A systematic study with different aldehydes revealed that an interaction between the double bond and the carbonyl group of the aldehyde is superior to minimization of steric hindrance in the transition state, thus leading to the desired C7-C8 anti relationship [53]. Later in the synthesis of epothilone B, in Danishefsky s approach, the triethylsilyl group was removed and the C3 ketone converted to the desired C3 alcohol by enantioselective catalytic Noyori reduction [10]. 

The most general route to terminal polyynes involves the use of a protecting group which can be readily removed after the coupling and, as in oxidative couplings, the triethylsilyl group is admirably suited to this purpose Thus, l-phenyl-4-... 

The TBS group then had to be replaced (two steps, Scheme 3 a and b) by the more easily removable TES (triethylsilyl) group to permit deblocking at the last step in the synthesis of himastatin. Before combination of the bisindolyl unit with the peptidal ester unit, several additional changes in the state of protection at the two nitrogens... 

The DPMS group has stability intermediate between the TMS and TFS (triethylsilyl) groups. It is incompatible with base, acid, BuLi, LiAlIL, pyridinium chlorochromate. 

The fact that hydrolysis of the OTMS group is so facile makes it unsuitable for most alcohol moieties that require long-term protection. A more stable silyl derivative is the triethylsilyl group (O— SiEt3, O—TES). 

In the examples shown in Schemes 2.19 and 2.20, neither the substrates nor the products were sensitive to elevated temperatures or acid and so dehydration was accomplished by azeotropic distillation. However, acetalisation of acid-sensitive substrates can be a major challenge. For example, a synthesis of the Crambescidin family of guanidine alkaloids was impeded by problems with the acid sensitivity of the ketone 2L1 [Scheme 2.21]. The triethylsilyl group made the desired acetalisation sluggish the firee alcohol reacted faster but it also underwent very easy -elimination. Conditions that accomplished removal of the triethylsilyl group and acetalisation without competing dehydration entailed reaction of 21.1 with the cyclic ortho ester 213 and 1,3-propanediol in the presence of Amberlyst-15 at room temperature in acetonitrile. The required hydro-... 

Regioselective reduction of the C-1 carboxylate of dimethyl (R)-malate (203) with BMS-NaBH4 followed by protection of the diol with either triethylsilyl groups or an acetonide furnishes 978. Condensation of the ester group with the anion of dimethyl methylphosphonate produces j -ketophosphonate 979 in high yield. Coupling of 979 with (2 S)-3-hydroxy-2-methylpropionate-derived aldehyde 980 under Homer—Emmons conditions affords 981, which contains the basic skeletal requirements for the C-16 to C-26 subunit (982) of hali-chondrin B (Scheme 144) [213]. 

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