Butyldimethylsilyl Iodide

Epoxides can be converted to allylic alcohols163 by treatment with several reagents, including lithium diethylamide,164 /-butyldimethylsilyl iodide,165 methylmagnesium N-cy-... 

The conversion of epoxides to allylic alcohols (Scheme 24) can also be considered here. A variety of reagents, including lithium diethylamide, r-butyldimethylsilyl iodide, a dialkylboryl triflate and an ethylaluminum dialkylamide have been used successfully. 

CH2CI2 to THF allowed protected diethyl l-(phenylsulfonyl)-3-hydroxy-4-iodobutylphosphonate to be prepared directly from the epoxide (Scheme 4.51). This reaction presumably proceeds via the generation in situ of iert-butyldimethylsilyl iodide. Similarly, diethyl 1-(ethoxycarbonyl)-3,4-epoxybutylphosphonate undergoes regioselective ring opening at C-4 by amines in DMF at 50°C. ... 

Reaction with Nucleophiles. TBDMSCl is the reagent of choice for the preparation of other TBDMS-containing reagents. For example, f-butyldimethylsilyl cyanide may be prepared by the reaction of TBDMSCl and potassium cyanide in acetonitrile containing a catalytic amount of zinc iodide. TBDMSCN has also been prepared by treatment of TBDMSCl with KCN and 18-crown-6 in CH2CI2 at reflux and by treatment of TBDMSCl with lithium cyanide prepared in situ. i-butyldimethylsilyl trifluoromethanesulfonate is prepared by treatment of TBDMSCl with trifluoromethanesulfonic acid at 60 °C. Other nucleophiles, such as thiolates, also react with TBDMSCl. f-butyldimethylsilyl iodide was prepared by treatment of TBDMSCl with sodium iodide in acetonitrile. In contrast to THF cleavage reactions using TMSI, the more stable TBDMS-protected primary alcohol may be isolated from the reaction in eq 12. 

Related Reagents. f-Butyldimethylchlorosilane triethylsi-lyl trifluoromethanesulfonate trimethylsilyl trifluoromethane-sulfonate f-butyldimethylsilyl iodide A -f-(butyldimethylsilyl)-W-methyltrifluoroacetamide triisopropylsilyl trifluoromethanesulfonate. 

Me3SiCH2CH=CH2i TsOH, CH3CN, 70-80°, 1-2 h, 90-95% yield. This silylating reagent is stable to moisture. Allylsilanes can be used to protect alcohols, phenols, and carboxylic acids there is no reaction with thiophenol except when CF3S03H is used as a catalyst. The method is also applicable to the formation of r-butyldimethylsilyl derivatives the silyl ether of cyclohexanol was prepared in 95% yield from allyl-/-butyldi-methylsilane. Iodine, bromine, trimethylsilyl bromide, and trimethylsilyl iodide have also been used as catalysts. Nafion-H has been shown to be an effective catalyst. 

Intermediate 10 must now be molded into a form suitable for coupling with the anion derived from dithiane 9. To this end, a che-moselective reduction of the benzyl ester grouping in 10 with excess sodium borohydride in methanol takes place smoothly and provides primary alcohol 14. Treatment of 14 with methanesulfonyl chloride and triethylamine affords a primary mesylate which is subsequently converted into iodide 15 with sodium iodide in acetone. Exposure of 15 to tert-butyldimethylsilyl chloride and triethylamine accomplishes protection of the /Mactam nitrogen and leads to the formation of 8. Starting from L-aspartic acid (12), the overall yield of 8 is approximately 50%, and it is noteworthy that this reaction sequence can be performed on a molar scale. 

The successful implementation of this strategy is shown in Scheme 4. In the central double cyclization step, the combined action of palladium(n) acetate (10 mol %), triphenylphosphine (20 mol %), and silver carbonate (2 equiv.) on trienyl iodide 16 in refluxing THF results in the formation of tricycle 20 (ca. 83 % yield). Compound 20 is the only product formed in this spectacular transformation. It is noteworthy that the stereochemical course of the initial insertion (see 17—>18) is guided by an equatorially disposed /-butyldimethylsilyl ether at C-6 in a transition state having a preferred eclipsed orientation of the C-Pd a bond and the exocyclic double bond (see 17). Insertion of the trisubstituted cycloheptene double bond into the C-Pd bond in 18 then gives a new organopal-... 

This silyl hydrazone formation-oxidation sequence was originally developed as a practical alternative to the synthesis and oxidation of unsubstituted hydrazones by Myers and Furrow [31]. The formation of hydrazones directly from hydrazine and ketones is invariably complicated by azine formation. In contrast, silyl hydrazones can be formed cleanly from /V,/V -bis(7< rt-butyldimethylsilyl)hydrazine and aldehydes and ketones with nearly complete exclusion of azine formation. The resulting silylhydrazones undergo many of the reactions of conventional hydrazones (Wolff-Kishner reduction, oxidation to diazo intermediate, formation of geminal and vinyl iodides) with equal or greater efficiency. It is also noteworthy that application of hydrazine in this setting may also have led to cleavage of the acetate substituents. 

The same research group also showed that the r-butyldimethylsilyl (TBDMS)-protected 4-substitued 4,5-dihydro-l,2,4-oxadiazol-5-one 192 afforded the alcohol 193 on treatment with ethanolic HC1. Mesylation and treatment of the intermediate with sodium iodide gave the iodofluoroalkenyl-substituted 4,5-dihydro-l,2,4-oxadiazol-5-one 194 (Scheme 26) <2004T10907>. 

A tandem enolate-arylation-allylic cyclisation, in which an essential z-butyldimethylsilyl ether protecting group delays the cyclisation step until the Pd-catalysed arylation is complete, enables 1-vinyl-l//-[2]benzopyrans 54 to be prepared from 2-bromobenzaldehyde (Scheme 32) <00CC1675>. 4-Substituted isochromans 55 are formed from aldehydes by a Pd-catalysed termolecular queuing cascade. The sequence involves cyclisation of an aryl iodide onto a proximate alkyne followed by an allene insertion. Transmetallation with indium then allows addition to the aldehyde (Scheme 33) . 

The potentiality of the present methodology is demonstrated by the synthesis of y-undecalactone, as shown in Scheme 18 [37,47], The treatment of the THP-protected cu-hydroxyalkyl iodide with the anion of methoxybis(trimethylsilyl) methane gave the corresponding alkylation product. Acidic deprotection of the hydroxyl group followed by Swern oxidation produced the aldehyde. The aldehyde was allowed to react with heptylmagnesium bromide, and the resulting alcohol was protected as tm-butyldimethylsilyl ether. The electrochemical oxidation in methanol followed by the treatment with fluoride ion afforded the y-undeealactone. 

Removal of the tri-wo-propylsilyl (TIPS) and tm-butyldimethylsilyl (TBS) protecting groups could be accomplished concomitantly with TBAF in tetrahydrofuran at 0 °C, but here competing elimination of the secondary bromide was observed. Better overall yields and cleaner conversion was observed when TBS ether was cleaved with 5 % aqueous HF in acetonitrile at 0 °C followed by removal of the acetylenic TIPS with TBAF under milder conditions of -78 °C.10 The diastereomers are not separated before the desilylation process therefore even a 3 1 mixture of E- and Z-enyne is obtained. Prelaureatin 4 and its F-isomer 17 are likewise goals in natural product synthesis. Crimmins and co-workers developed an own synthetic route to 4. The reaction sequence is similar up to aldehyde 55. Afterwards a Z-vinyl-iodide is selectively formed and the alkyne is introduced via a Sonogashira reaction. 

Enol silyl ethers Bromomagnesium diiso-propylamide. f-Butyldimethylchlorosilane. r-Butyldimethylsilyl trifluoromethanesul-fonate. Chlorotrimethylsily 1-Sodium iodide. Iron. Lithium f-octyl-t-butylamide. 

Cyclic vinyloxiranes were opened with r-butyldimethylsilyl cyanide to yield isonitriles, as shown in equation (50). °° The opening of vinyloxiranes like (142) with TMS-I, TMS-I/TiCU and Smh was attempted in an effort to provide a topographical option for the [2 + 3] dihydrofuran annulation. While the 2,5-substitution pattern inherent in (143) is furnished through thermolytic rearrangements, the 2,3-isomer would result from an 5n2 opening of (142) to allylic iodide (154), which would cyclize to 2,3-function-... 

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