Alkyl Silyl Ethers Research Articles

NFSI/KF mediated mild and chemoselective interconversion of aryl TBDMS ethers to their benzene sulfonate

A one pot protocol for the transformation of aryl TBDMS ethers to corresponding benzene sulfonate esters using NFSI (N-flurobenzenesulfonimide)/KF is described. In situ generation of benzenesulfonyl fluoride directs chemoselective cleavage of aryl silyl ethers over alkyl silyl ethers. Electron withdrawing substituent’s on aryl ring provided better yield than donating groups. Protecting groups and sensitive functionalities are well tolerated in this methodology. Thus, commercially available inexpensive reagents, mild reaction conditions and step economy are the advantages of this method.

Functionalization of 1,3-diphosphacyclobutadiene cobalt complexes via Si–P bond insertion

AbstractWe report the synthesis of functionalized 1,3-bis(diphosphacyclobutadiene) complexes via the insertion of carbon-oxygen bonds of ethers, esters, aldehydes and amides into the P–Si bond of silylated complexes. Reactions of [K(tol)2][Co(η4-P2C2R2)2] [[K(tol)2][1a]:R=tBu,[K(tol)2][1b]:R=tPent (=tert-pentyl)] with Me3SiCl afford the trimethylsilyl-substituted derivatives [Co(η4-P2C2R2SiMe3)(η4-P2C2R2)] (2a,b, R=tBu,tPent). The Me3Si group is connected to a phosphorus atom of one of the 1,3-diphosphacyclobutadiene ligands.2a,breadily react with organic substrates containing C–O single and C=O double bonds at ambient temperature. [Co(η4-P2C2R2(CH2)4OSiMe3)(η4-P2C2R2)] (3a,b) are formed by reaction of2a,bwith traces of THF. They can also be isolated by reacting the THF solvates [K(thf)2{Co(P2C2tBu2)2}] ([K(thf)2][1a]) and [K(thf)3{Co(P2C2tPent2)2}] ([K(thf)3][1b]) with Me3SiCl in toluene or THF. The adamantyl-substituted complex [Co(η4-P2C2Ad2(CH2)4OSiMe3)(η4-P2C2Ad2)] (3c) was prepared analogously from [K(thf)4{Co(P2C2Ad2)2}] and Me3SiCl.[K(thf)2][1a]reacts cleanly with Ph3SnCl affording [Co(η4-P2C2tBu2SnPh3)(η4-P2C2tBu2)] (4) in high yield. Reaction of2awith styrene oxide affords [Co(η4-P2C2tBu2PhC2H3OSiMe3)(η4-P2C2tBu2)] (5) as a single regioisomer. By contrast, multinuclear NMR spectroscopic studies indicate mixtures of two isomeric insertion products6/6′ and7/7′, respectively, which result from the insertion of 1,2-epoxy-2-methylpropane and 1,2-epoxyoctane. Moreover, these monitoring studies show that reactions of2awith acyclic ethers afford alkyl substituted complexes such as [Co(η4-P2C2tBu2Et)(η4-P2C2tBu2)] (8) and alkylsilyl ethers. Reaction of2awithγ-butyrolactone gives [Co(η4-P2C2tBu2(CH2)3C(O)OSiMe3)(η4-P2C2tBu2)] (9) via cleavage of the endocyclic C–O single bond of the lactone. Benzaldehyde and acetone cleanly react with2ato [Co(η4-P2C2tBu2CH(Ph)OSiMe3)(η4-P2C2tBu2)] (10) and [Co(η4-P2C2tBu2CMe2OSiMe3)(η4-P2C2tBu2)] (11), while the sterically more demanding ketones 3-pentanone and acetophenone selectively yield the known hydride complex [Co(η4-P2C2tBu2)2H] (A). Phenyl isocyanate reacts with2aat elevated temperature to form [Co(η3-P2C2tBu2CON(Ph)SiMe3)(η4-P2C2tBu2)] (12) with a functionalizedη3-coordinated ligand.[K(tol)2][1a],[K(tol)2][1b],2a,2b,3a–c,4,5, and9–12were isolated and characterized by multinuclear NMR spectroscopy, UV/Vis spectroscopy and elemental analysis.[K(tol)2][1b],2a,2b,3c,4,5, and9–12were additionally characterized by X-ray crystallography.

Reductive Degradation of Lignin and Model Compounds by Hydrosilanes

The exploitation of lignin, the second most abundant naturally occurring polymer on earth, has been hampered by its network structure, which makes it difficult to process. Hydrosilanes have previously been shown to convert aryl ethers to hydrolyzable silyl ethers in the presence of B(C6F5)3. We demonstrate that the process is general and can be used to convert model lignin compounds to both aryl silyl ethers and alkanes. The relative reactivity of functional groups on model lignin compounds was found to be phenol > primary alcohol > methoxybenzene > alkyl silyl ethers. The process thus leads to cleavage of β-O-4, α-O-4, and methoxybenzene groups with concomitant silylation of phenolic and secondary alcohol groups. At longer time points provided sufficient silane was present, the full reduction of primary and secondary alcohols to alkyl groups was observed. Softwood lignin itself could only be partially solubilized (∼30%) even using excess hydrosilane and high catalyst loadings; the products were not characterized in detail. The lack of further degradation was attributed to its highly branched network structure containing 5-5, β-5, 4-O-5, and other linkages derived from coniferyl alcohol monomers that are not susceptible to reductive silylation. By contrast, over 95% of hardwood lignin was efficiently reduced/degraded into organosoluble products by the monofunctional hydrosilane HMe2SiOSiMe3 over a few hours at 50 °C. The molecular weight of the silylated products was consistent with oligomeric structures comprised of 3–8 linked aryl groups. This process holds promise to increase the accessibility to value-added products using lignin as a starting material.

Hydration of Terminal Alkynes Catalyzed by Water-Soluble Cobalt Porphyrin Complexes

Water-soluble cobalt(III) porphyrin complexes were found to promote the hydration of terminal alkynes to give methyl ketones. The alkyne hydration proceeded in good to excellent yield with 0.1 to 2 mol % cobalt catalyst 1 and was compatible with the presence of acid/base- or redox-sensitive functional groups such as alkyl silyl ethers; allyl ethers; trityl ethers; benzyl ethers; carboxylic esters; boronic esters; carboxamides; nitriles; and nitro, iodo, and acetal groups. Some of the alkyne substrates tested here are otherwise difficult to hydrate. The alkyne hydration can be performed on a gram scale, and the catalyst can be recovered by aqueous workup.

A Novel, Chemoselective and Efficient Microwave-Assisted Deprotection of Silyl Ethers with Selectfluor

A novel microwave-assisted, chemoselective and efficient method for the cleavage of silyl ethers (aliphatic and aromatic) catalyzed by Selectfluor is reported. A wide range of TBS-, TIPS-, and TBDPS-protected alkyl silyl ethers can be chemoselectively cleaved in high yield in the presence of aryl silyl ethers. The chemoselective deprotection of phenolic TBS ethers, and not the TIPS- or TBDPS-protected phenolic ethers, and the deprotection of silyl esters were also achieved under these reaction conditions. In addition, the transetherification and etherification of benzylic hydroxy groups in alcoholic solvents is observed.

A mild and efficient approach for the selective deprotection of benzyl and phenyl trimethylsilyl ethers in 1-butyl-3-methyl-imidazolium chloride

1-Butyl-3-methyl-imidazolium chloride ([bmim]Cl) in the absence of any catalyst mediated the selective deprotection of benzyl and phenyl trimethylsilyl (TMS) ethers to the corresponding alcohols and phenol in good yields at room temperature even in presence of alkyl silyl ethers. The work-up of reactions is very simple and the products do not require further purification. The ionic liquid (IL) can be recycled and reused for several runs without any significant loss of activity.

DBU-Promoted Facile, Chemoselective Cleavage of Acetylenic TMS Group

Acetylenic trimethylsilyl (TMS) groups were efficiently removed using 1,8-diazabicyclo[5.4.0]undec-7-ene (DBU). With either 1.0 or even 0.1 equivalents of DBU, smooth desilylation of various terminal acetylenic TMS groups was accomplished selectively in the presence of alkyl silyl ethers and other base-labile groups. Furthermore, more sterically hindered terminal acetylenic silyl groups such as TBDMS and TIPS remained intact under these conditions.

The chemoselective and efficient deprotection of silyl ethers using trimethylsilyl bromide

An efficient and chemoselective cleavage of silyl ethers (primary, secondary and aromatic) by using catalytic quantities of trimethylsilyl bromide (TMSBr) in methanol is reported. A wide range of alkyl silyl ethers such as TBS, TIPS, and TBDPS can be chemoselectively cleaved in high yield in the presence of aryl silyl ethers. The deprotection of silyl esters was also achieved employing catalytic quantities of TMSBr.

DBU-Mediated Mild and Chemoselective Deprotection of Aryl Silyl Ethers and Tandem Biaryl Ether Formation

An efficient method for the selective cleavage of aryl ­silyl ethers is established using 1,8-diazabicyclo[5.4.0]undec-7-ene (DBU). With either 1.0 or 0.10 equivalent of DBU, smooth de­silylation of various aryl silyl ethers was accomplished selectively in the presence of alkyl silyl ethers and other base-sensitive groups such as acetate and ester. In addition, direct transformation of aryl silyl ethers into biaryl ethers using a catalytic amount of DBU was possible through tandem desilylation and SNAr reaction with ­activated aryl fluorides.

Rapid, Acid‐Mediated Deprotection of Silyl Ethers Using Microwave Heating

Microwave heating of triethylsilyl (TES)‐ and tert‐butyldimethylsilyl (TBS)‐protected 1° and 2° alcohols in a mixture of equal parts acetic acid, tetrahydrofuran (THF), and water allows deprotection in as little as 5 min. tert‐butyldiphenylsilyl (TBDPS)‐ and triisopropylsilyl (TIPS)‐protected alcohols and silyl‐protected phenols are stable in these conditions. Thus, selective deprotection of TES‐ and TBS‐protected alcohols in the presence of TIPS or TBDPS ethers is possible. Similarly, alkyl silyl ethers can be deprotected in the presence of aryl silyl ethers.

An Efficient and Convenient Method for the Direct Conversion of Alkyl Silyl Ethers into the Corresponding Alkyl Ethers Catalyzed by Iron(III) Chloride.

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An Efficient and Convenient Method for the Direct Conversion of Alkyl Silyl Ethers into the Corresponding Alkyl Ethers Catalyzed by Iron(III) Chloride

Various alcohol silyl ethers were readily and efficiently transformed into the corresponding alkyl ethers in high yields by the use of aldehydes combined with triethylsilane in the presence of a catalytic amount of iron(III) chloride.

BiOClO4‐Mediated Deprotection of Silyl Ethers.

Abstract TES- and TBS-protected alcohols undergo deprotection in good to excellent yield upon heating with 1 equiv of BiOClO 4 - x H 2 O in CH 2 Cl 2 . TBDPS- and TIPS-protected 2° alcohols are more resistant to deprotection. The use of this method in selective desilylation is, however, limited to the deprotection of alkyl silyl ethers in the presence of TBDPS-protected phenols.

A Convenient Method for Protection and Deprotection of Alcohols and Phenols as Alkylsilyl Ethers Catalyzed by Iodine under Microwave Irradiation.

AbstractFor Abstract see ChemInform Abstract in Full Text.

BiOClO4-mediated deprotection of silyl ethers

TES- and TBS-protected alcohols undergo deprotection in good to excellent yield upon heating with 1equiv of BiOClO4-xH2O in CH2Cl2. TBDPS- and TIPS-protected 2° alcohols are more resistant to deprotection. The use of this method in selective desilylation is, however, limited to the deprotection of alkyl silyl ethers in the presence of TBDPS-protected phenols.

Graphical Abstracts

Synth. Commun. 2003, 33, 4005 A Convenient Method for Protection and Deprotection of Alcohols and Phenols as Alkylsilyl Ethers Catalyzed by Iodine Under Microwave Irradiation Ira Saxena,1 Nabajyoti Deka,1 Jadab C. Sarma,1,* and Sadao Tsuboi2,* 1Organic Chemistry Division, Regional Research Laboratory, Jorhat, Assam, India; 2Department of Environmental Chemistry and Materials, Okayama University, Okayama, Japan Irradiation of alcohols or phenols with tert-butyldimethylsilyl chloride (TBDMSCl) or trimethylsilyl chloride (TMSCl) in presence of catalytic amount (20 mol%) of iodine in a microwave oven for 2 min gives the corresponding silyl ethers in excellent yield. Iodine in methanol deprotects the silyl ether into its parent alcohol or phenol under similar reaction conditions.

A Convenient Method for Protection and Deprotection of Alcohols and Phenols as Alkylsilyl Ethers Catalyzed by Iodine Under Microwave Irradiation

Irradiation of alcohols or phenols with tert-butyldimethylsilyl chloride (TBDMSCl) or trimethylsilyl chloride (TMSCl) in presence of catalytic amount (20 mol%) of iodine in a microwave oven for 2 min gives the corresponding silyl ethers in excellent yield. Iodine in methanol deprotects the silyl ether into its parent alcohol or phenol under similar reaction conditions.

OXIDATION DEPROTECTION OF TRIMETHYLSILYL ETHERS TO CARBONYL COMPOUNDS BY NaBrO3-NH4Cl REAGENT IN AQUEOUS ACETONITRILE

Primary and secondary benzylic and secondary alkyl trimethlysilyl ethers are efficiently converted into their carbonyl compounds by NaBrO3-NH4Cl in aqueous acetonitrile. Primary alkyl silyl ethers give only the corresponding alcohols without further oxidation with NaBrO3-NH4Cl.

A novel and efficient method for the silylation of alcohols with methallylsilanes catalyzed by Sc(OTf) 3

Reaction of alcohols with methallylsilanes in the presence of a catalytic amount of Sc(OTf) 3 provides efficiently the corresponding alkyl silyl ethers. By using microencapsulated (MC) Sc(OTf) 3, which can be easily recovered and reused, yields of alkyl silyl ethers are improved and the work-up process after completion of the reaction is considerably simplified.

Selective deprotection of silyl-protected phenols using solid NaOH and a phase transfer catalyst

Aryl silyl ethers can be deprotected to yield phenols in good to excellent yields using a biphasic system of 10 equivalents of NaOH and catalytic Bu 4NHSO 4 in 1,4-dioxane. Alkyl silyl ethers prepared using a variety of silyl protecting groups survive under these conditions, allowing selective deprotection of silyl-protected phenols in the presence of silyl-protected alcohols.