16: Silylethers

Deprotection of N-SEM from Protected Thymidine Dinucleoside To a cold solution of protected dinucleoside 3 or 6 (100 mg, 0.11 mmol) in methylene chloride (10 mL), tin tetrachloride 1M (1.5 mL) in ...Personally I mistrust TBAF because of workup weirdness, but that's not so much related to reaction conditions. My first-try deprotection procedure for TMS-acetylene deprotection would be KF suspended/partially dissolved in DMF, at room temp, give it a few hours it'll probably go completely.Nelson and Crouch, "Selective Deprotection of Silyl Ethers", Synthesis, , -. Summary of Silyl Ether Protecting Groups Provide a mechanism for the formation of a silyl ether.

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Effective deprotection of 2

 · In essence, the procedure combines the virtues of (1) using a com~ierciaily available source of fluoride [n-Bu4NF (TBAF) in THF] (2) substituting EN-dimethyipropyleneurea (DMPU) for HMPA without noticeable decreases in rates of deprotections; (3) theA mild and efficient protocol for the deprotection of silyl ethers using KF in tetraethylene glycol is reported. A wide range of alcoholic silyl ethers can be selectively cleaved in high yield in the presence of certain acid- and base-labile functional groups. Moreover, the · The selection of a protective group is an important step for achievement of a multistep organic synthesis. 2- (Trimethylsilyl)ethoxymethyl (SEM) group was developed) as a useful protective group which was stable over a wide range of conditions and could be cleaved in the presence of fluoride ion.

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experimental chemistry

New lability and stability sequences have been established for multifunctional substrates containing SEM ether group(s) by a MgBr 2 /Et 2 O/MeNO 2 deprotection protocol. In papers with more than one author, the asterisk indicates the name of the author to whom inquiries about the paper should be addressed.Deprotection for 0.2 µmole Synthesis Scale Reagents • TBAF Tetrabutylammonium fluoride. Using either a 1 M TBAF solution in an aprotic solvent or prepare 15 % TBAF in same solvent • Aprotic solvents: THF, DMF, NMP or DMSO • 1 M Tris pH 7.4 · CsF or KF or NH4F may do the deprotection job as well as TBAF while they will not mess up in your column. I remember KF will work in acetonitrile. HF is acidic and may decompose your compound. HF-Pyridine is almost equally messy in column as TBAF a.

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(PDF) An Efficient Deprotection of N …

Personally I mistrust TBAF because of workup weirdness, but that's not so much related to reaction conditions. My first-try deprotection procedure for TMS-acetylene deprotection would be KF suspended/partially dissolved in DMF, at room temp, give it a few hours it'll probably go completely.2-(Trimethylsilyl)ethoxymethyl Esters (SEM) Stability: Cleavage:SEM is removed with fluoride (e.g. TBAF in DMF) Stable to Acid 2-(Trimethylsilyl)ethyl Esters Benzyl Esters Helv Chim Acta , 60, RCO2HHO O SiMe3 O O SiMe3 R O RCO2H HO SiMe 3Deprotection of N-SEM from Protected Thymidine Dinucleoside To a cold solution of protected dinucleoside 3 or 6 (100 mg, 0.11 mmol) in methylene chloride (10 mL), tin tetrachloride 1M (1.5 mL) in.

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TBAF Fluorination for Preparing Alkyl Fluorides

allowing a wide variety of both reaction and deprotection conditions. The leaving group also plays an important role in the reactivity and use of silylating reagents. Whilst chlorotrimethylsilane [product code: ] liberates hydrogen chloride on reaction, otherDeprotection of N-SEM from Protected Thymidine Dinucleoside To a cold solution of protected dinucleoside 3 or 6 (100 mg, 0.11 mmol) in methylene chloride (10 mL), tin tetrachloride 1M (1.5 mL) in ... · Here we will review fluorinations with the readily available and prototypical nucleophilic fluorinating reagent tetrabutylammonium fluoride (TBAF) and its derivatives. In the gas phase, fluoride is an incredibly potent nucleophile and strong base because of its concentration of charge (as the smallest monoanion) and because of its propensity to form very strong bonds with hydrogen and carbon.

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Chapter 3 Protecting Groups

 · It gives the concise and complete protecting and deprotecting groups. A protecting group or protective group is introduced into a molecule by chemical modification of a functional group to obtain chemoselectivity in a subsequent chemical reaction. It plays andeprotection times, especially when multiple ones are present, and the Tmob group is difficult to scavenge. How ever, the Trt group is readily r moved and easily scavenged. N-terminal Asn(Trt) may need extended cleavage times4,10. Use of the fasterN-terminal . ...Common reagents for deprotection: TBAF, BF3, KF, or pyridine-HF Trimethylsilyl (TMS) Can be cleaved with K2CO3, MeOH or ... General Mechanism 12 (i) For selection between 1,3-diol and trans-1,2-diol O O vs. O HO O HO O R O R (ii) For selectioncis-1,2.

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PROTECTING GROUPS IN ORGANIC SYNTHESIS

 · Such understanding is acquired through experience and knowledge of reaction mechanism and reaction stereochemistry. To illustrate the purpose and practice of protecting groups in organic synthesis, let us suppose that the synthesis of cis -2-octene, which we outlined in Section 13-7, has to be adapted for the synthesis of 5-octyn-1-ol. · SEM group which has in fact been characterized as "rugged". 2b Typical deprotection conditions are TBAF in HMPA3 (or nontoxic equivalents),4 and activated fluoride ion (CsF) at elevated temperature.5 Other deprotection protocols have been suggested.6Protecting Groups: A Necessary Evil 3 Note, however, that each protecting group incorporated in a multi-step synthesis increases the synthesis by two non-productive steps reducing the overall yield and efficiency of the synthesis. Protecting Groups in Organic.

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Chapter 3 Protecting Groups

! ! iii! Tetrabutylammonium fluoride (TBAF) has been recently discovered to catalyze regioselective deacylation of cellulose esters of the secondary alcohols at C-2 and C-3. The kinetic isotope effects in this deacylation reaction have been investigated to reveal the · New conditions for effective cleavage of SEM ethers were developed (TBAF/HMPA in the presence of MS 4A) and usefulness of this reaction was demonstrated by the synthesis of thyrsiferyl-23 acetate. Tetrahedron Letters,Vo1.29,No.42,pp -, ...Common reagents for deprotection: TBAF, BF3, KF, or pyridine-HF Trimethylsilyl (TMS) Can be cleaved with K2CO3, MeOH or ... General Mechanism 12 (i) For selection between 1,3-diol and trans-1,2-diol O O vs. O HO O HO O R O R (ii) For selectioncis-1,2.

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Studies on the Deprotection of Triisopropylsilylarylacetylene Derivatives

ylsilylacetylene as the acetylene source and TBAF functioning as a base, activator, and deprotection reagent (blue route, Scheme 1). In addition to significantly reducing the synthetic burden from a 3 step synthesis with a long overall reaction time to a single 3Protecting Groups in Organic Synthesis-2 Ready Brook Rearrangement bond BDE (kcal/mol) CSi OSi FSi 69 103 141 question: using approx. pKa values and the BDE above, estimate Keq for different R's in the equation 1. O X RStudies on the Deprotection of Triisopropylsilylarylacetylene Derivatives 135expensive way [24]. Thus, a more economical method is still needed. Experimental Section Protected arylalkynes 1, 2, 4a-c, 6, 8 and 10 used in this study were prepared according to a.

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cyclo

 · Here we will review fluorinations with the readily available and prototypical nucleophilic fluorinating reagent tetrabutylammonium fluoride (TBAF) and its derivatives. In the gas phase, fluoride is an incredibly potent nucleophile and strong base because of its concentration of charge (as the smallest monoanion) and because of its propensity to form very strong bonds with hydrogen and carbon.Deprotection for 0.2 µmole Synthesis Scale Reagents • TBAF Tetrabutylammonium fluoride. Using either a 1 M TBAF solution in an aprotic solvent or prepare 15 % TBAF in same solvent • Aprotic solvents: THF, DMF, NMP or DMSO • 1 M Tris pH 7.4 · Other sources of fluoride ion that did not effect deprotection include TBAF (in THF or DMPLO, CsF fin DIVlF, CHaCN, or THF), and Bu, N-BF4 (in THF or DMPLO. Use of LiBF4 in CH3CN removes the cydo-SEM group very easily, although in our hands, this reagent/solvent combination, in control experiments, also deprotects standard dioxane and dioxolane derivatives.

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