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Triisopropylsilyl function

Silyl-derived protective groups are also used to mask the thiol function. A complete compilation is not given here, since silyl derivatives are described in the section on alcohol protection. The formation and cleavage of silyl thioethers proceed analogously to those of simple alcohols. The Si-S bond is weaker than the Si-O bond, and therefore, sulfur derivatives are more susceptible to hydrolysis. For the most part, silyl ethers are rarely used to protect the thiol function, because of their instability. Silyl ethers have been used for in situ protection of the-SH group during amide formation. The use of the sterically demanding and thus more stable triisopropylsilyl thioether may prove worthwhile. ... [Pg.482]

It was anticipated all along that the vinylsilane residue could serve as a vinyl iodide surrogate. After protection of the C-14 secondary hydroxyl in 180 in the form of a triisopropylsilyl ether, the vinyltrimethylsilyl function can indeed be converted to the requisite vinyl iodide with AModosuccinimide (NIS) (see 180—>181, Scheme 43). Vinyl iodide 181 is produced stereospecifically with retention of the A17,18 double bond geometry. This transformation is stereospecific since the stereochemistry of the starting vinylsilane and the vinyl iodide product bear a definite relationship to each other.67b 75... [Pg.608]

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]. [Pg.270]

Magnus and coworkers have published full details55 on the direct a- or /J-azido functionalization of triisopropylsilyl (TIPS) enol ethers using an iodosylbenzene-TMS-azide combination (equation 13) the w-pathway, favoured at —78 °C, is an azide radical addition process, whereas the -pathway, favoured at —15 to — 20 °C, involves ionic dehydrogenation. Attempts to extend the /3-functionalization to other TMSX derivatives failed. [Pg.1673]

The /J-azido triisopropylsilyl (TIPS) enol ether (96) functionalization developed by Magnus et al. from TIPS-enol ether (95) using iodosobenzene (Phl=0)-TMSN3 [70-73] provides a unique strategy for the total synthesis of an antitumor agent, (+)-pancratistatin (97) [Eq. (21)]. [Pg.219]

The triisopropylsilyl (TIPS) group is introduced under the same conditions as TBS groups.5 Instead of imidazole DMAP can be used, too. Under these conditions only the primary alcohol functionality is selectively protected as TIPS ether. [Pg.269]

During a monumental synthesis of Strychnine, the Overman group encountered difficulties with the simple selective protection of the primary alcohol function in diol 87,1 as its TIPS ether [Scheme 4.89].143 The best method involved treatment of diol 87.1 with 2 equivalents of triisopropylsilyl chloride and 2.2 equivalents of 1,1,3,3-tetramethylguanidine at 0 °C in N-methylpyrrolidinone until the diol could no longer be detected by thin layer chromatography. This treatment... [Pg.228]

Control of the absolute stereochemistry was possible starting from the optically active substrate. Initial attempts by protecting the hydroxy function as a j8-oxo ester were unsuccessful146. However, the use of triisopropylsilyl protective group allowed the diastereoselective preparation of the vinylaziridine which was then converted to 6,7-diepicastanospermine140. [Pg.943]

Nitro-l,l-bis(triisopropylsilyl)benzocyclopropenc underwent several functional group modifications with preservation of its structure. Reduction with zinc/hydrochloric acid gave the 3-amino derivative 3a which was acetylated with acetyl chloride. Reduction with lithium aluminum hydride gave l,l,l l -tetrakis(triisopropylsilyl)-3,3 -azobenzocyclopropene (4) in 7.5% yield. When l,l-bis(triisopropylsilyl)benzocyclopropen-3-amine (3a) was reacted with nitrous acid, the coupling product 4-amino-l,l,r,r-tetrakis(triisopropylsilyl)-3,3 -azabenzocyclo-propene (5) was formed in 14% yield. [Pg.2905]

The reaction conditions were sufficiently mild that a broad range of functional groups and substitution patterns were tolerated including cyclopropyl carbi-nyl ethers, benzyl (Bn), TIPS (triisopropylsilyl), and TBDPS (terf-butyldiphe-nylsilyl) ethers Eq. (4), Table 1. However, steric congestion close to the reacting olefin resulted in a decrease in enantioselectivity, entry 3, giving the cyclohexenol in 81% yield and 84% ee. [Pg.336]

Very electron-rich aromatic systems interact with acid chlorides and anhydrides in the absence of a catalyst to afford good yields of ketones. Reactions of pyrrole and substituted pyrroles exemplify these reactions. The oxalylation shown in equation (18) was part of the synthesis of a complex, highly functionalized antitumor agent. Use of the triisopropylsilyl group to direct reaction to the 3-position (equation 19) is noteworthy. ... [Pg.739]

This unusual /3-azido functionalization of triisopropylsilyl ethers is a general reaction, although the best conditions show some variation with the structure of the enol silyl ether. [Pg.378]

Magnus reported the direct a- and )9-azido functionalization of triisopropylsilyl enol ethers using trimethylsilylazide and iodosylbenzene. In this mechanistically complex reaction sequence, it is believed that azidation of a carbon centered radical is occurring [78],... [Pg.607]

Khalafi-Nezhad et al. [18] achieved silylation of the 5 -hydroxyl function of uridine by use of imidazole and triisopropylsilyl chloride in a microwave oven at 200 W for 60 s, obtaining 80% yield of silylated product. The same reaction in dime-thylformamide with conventional heating [19] gave a 76% yield of silylated product after 24 h. [Pg.585]


See other pages where Triisopropylsilyl function is mentioned: [Pg.634]    [Pg.634]    [Pg.57]    [Pg.69]    [Pg.153]    [Pg.72]    [Pg.128]    [Pg.711]    [Pg.237]    [Pg.672]    [Pg.2488]    [Pg.95]    [Pg.540]    [Pg.69]    [Pg.97]    [Pg.65]    [Pg.72]    [Pg.193]    [Pg.14]    [Pg.61]    [Pg.481]    [Pg.390]    [Pg.1065]    [Pg.303]    [Pg.67]    [Pg.6]    [Pg.7]    [Pg.204]    [Pg.143]    [Pg.179]    [Pg.181]   
See also in sourсe #XX -- [ Pg.150 ]




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Triisopropylsilyl

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