Tert-butyl benzyl ether

This free-radical acylation approach is extended for the synthesis of a-keto esters and ketones using phenylsulfonyl methoxycarbonyl oxime ether 5 [23] and bis-methanesulfonyl oxime ether 6, respectively (Scheme 6) [24], 5 is more reactive and effective than 2b. For instance, radical reaction of tert-butyl iodide with 5 gave tert-butyl oxime ester in 65% yield, whereas the use of 2b gave the corresponding tert-butyl oxime ether in 15% yield. In free-radical-mediated ketone synthesis via a sequential radical acylation approach, 6 is used as a carbonyl equivalent geminal radical acceptor. This method works well with primary alkyl iodides but somewhat less efficiently with secondary iodides and can be applied to prepare unsymmetrical acyclic ketones as well as cyclic ketones. It is noteworthy that stable allylic and benzylic radicals react smoothly with 6. 

On the other hand, benzyl ethers react with NO in the presence of the NHPI catalyst to afford the corresponding aromatic aldehydes (Eq. (6.29)) [170]. The reaction of 4-methoxymefhyltoluene catalyzed by NHPI (10mol%) under NO (1 atm) for 5 h leads to p-tolualdehyde in 50% yield, tert-Butoxymethyltoluene and terf-butyl benzyl ethers are converted into the corresponding aldehydes in good yields. 

Both methyltriethylphosphonium fluoride and methyltributylphospho-nium fluoride have been prepared The latter generates benzyl fluoride from benzyl chloride in 80% yield and ethyl fluoroacetate from ethyl bromoacetate in 53% yield Methyltnbutylphosphonium fluoride converts 1-bromododecane to a 50 50 mixture of 1-fluorododecane and 1-dodecene Methyltnbutylphosphonium fluoride also quantitatively forms styrene from 1-bromo-1-phenylethane [26] Methyl-tnbutylphosphonium fluonde is the reagent of choice for the conversion of N,N dimethylchloroacetamide to its fluoride, but it is not able to convert chloro-acetonitnle to fluoroacetomtrile Methyltnbutylphosphonium fluoride changes chloromethyl octyl ether to the crude fluoromethyl ether in 66% yield The stereoselectivity of methyltnbutylphosphonium fluoride is illustrated by the reac tions of the 2-tert-butyl-3-chlorooxiranes [27] (Table 2)... 

The use of iodotrimethylsilane for this purpose provides an effective alternative to known methods. Thus the reaction of primary and secondary methyl ethers with iodotrimethylsilane in chloroform or acetonitrile at 25—60° for 2—64 hours affords the corresponding trimethylsilyl ethers in high yield. The alcohols may be liberated from the trimethylsilyl ethers by methanolysis. The mechanism of the ether cleavage is presumed to involve initial formation of a trimethylsilyl oxonium ion which is converted to the silyl ether by nucleophilic attack of iodide at the methyl group. tert-Butyl, trityl, and benzyl ethers of primary and secondary alcohols are rapidly converted to trimethylsilyl ethers by the action of iodotrimethylsilane, probably via heterolysis of silyl oxonium ion intermediates. The cleavage of aryl methyl ethers to aryl trimethylsilyl ethers may also be effected more slowly by reaction with iodotrimethylsilane at 25—50° in chloroform or sulfolane for 12-125 hours, with iodotrimethylsilane at 100—110° in the absence of solvent, " and with iodotrimethylsilane generated in situ from iodine and trimcthylphenylsilane at 100°. ... 

The same general method has been used by the submitters to prepare o-tolyl tert-butyl ether, m-tolyl feri-butyl ether, benzyl teri-butyl ether, and -anisyl fer/-butyl ether. 

Some of the polymers slowly change their helicity in solution. A chiral crown ether-potassium ferf-butoxide combined system was reported to cause polymerization of methyl, tert-butyl, and benzyl methacrylate to form isotactic polymers that had high rotation values (164). Detailed scrutiny, however, raised questions about the result (135, 165). At first, in the presence of the initiator, the oligomers exhibit considerable activity, but after removal of the catalyst, the optical activity decreases. This decrease may be attributed to unwinding of the helixes in the chain the helicity could be caused by the anchored catalyst. 

Entry 9 in Table 3.13 is an example of a safety-catch linker, which requires activation by TFA-mediated cleavage of a tert-butyl ether. The unactivated 2-(tm-butoxyj-phenyl esters are cleaved by amines 700 times more slowly than the corresponding 2-hydroxyphenyl esters [289]. A similar linker has been described [290], in which a benzyl ether is used instead of a ferf-butyl ether. Activation of this linker by debenzy-lation was achieved by treatment with HF or HBr/TFA [290]. 

The present procedure is the best way of preparing aliphatic isocyanides boiling above ethyl isocyanide. It has been applied to the synthesis of the following isocyanides 6 isopropyl (38%), -butyl (61%), tert-butyl (68%), and benzyl (56%). In preparing isopropyl isocyanide or ferf-butyl isocyanide, the petroleum ether should be of boiling point 30-35°, as otherwise it is difficult to separate these low-boiling isocyanides in the indicated yield, and,... 

Imidazole or pyridine mediated silylation of l,2-0-[l-exo-ethoxy )ethylidene]-oc-D-glucopyranose failed to give a high yield of the 6-silyl ether due to some polymerization and side reactions. Activation of hydroxyl groups via a tributylstannyl intermediate followed by the tetrabutylammonium bromide catalyzed reaction with tert-butyl-chlorodiphenylsilane was more successful [231], the 6-0-silyl derivative being isolated in 87 % yield.. The lability of this protecting group under benzylation with benzyl bromide and sodium hydride at 0 °C has been observed [449]. 

Potassium Benzyl bromide Benzyl tert-butyl ether Potassium... 

The acid 350 was demethylated with pyridine hydrochloride, then realkylated with benzyl bromide in aqueous potassium hydroxide to give 351. The latter was converted to the diazoketone 352 by the sequential treatment of 351 with oxalyl chloride and etheral diazomethane. Reaction of 352 with concentrated hydrobromic acid gave the bromoketone 353. The latter was reduced with sodium borohydride at pH 8 -9 to yield a mixture of diastere-omeric bromohydrins 354. Protection of the free hydroxyl as a tetrahydro-pyranyl ether and hydrogenolysis of the benzyl residue afforded 355. The phenol 355 was heated under reflux with potassium m/V-butoxide in tert-butyl alcohol for 5 hr to give a 3 1 epimeric mixture of dienone ethers 356 and 357 in about 50% yield. Treatment of this mixture with dilute acid gave the epimeric alcohols 358 and 359. This mixture was oxidized with Jones reagent to afford the diketone 349. 

Under these optimized conditions, di-tert-butylsilylene could be transferred to a range of acyclic and cyclic olefins (Schemes 7.9 and 7.10).11,74 The method was not sensitive to the steric nature of the R substituent nearly quantitative silylene transfer to olefins bearing ra-butyl, isopropyl, or tert-butyl groups was observed. Vinylsilanes were also tolerated as substrates. Olefins containing silyl ether, benzyl ether, and pivolate substituents were all effective traps of di-tm-butylsilylene. 

The solvent effect has long been recognized as an important factor in that it affects the lithium-oxygen bond polarization but also the electrophilic reagent380,398. The effect on aggregation was evaluated by measurement and comparison of the reactivities of monomeric, dimeric and tetrameric forms of LiPhIBP and LiPhAT or LiPhIBP in various ethers252. In the less polar solvent methyl-tert-butyl ether, lithium enolates are tetrameric and do not react with benzyl bromide. On the contrary, with added HMPA the dissociation of the tetrameric LiPhIBP is accompanied by solvation of each monomer by 1 -2... 

Acid-catalysed alkylation of an alcohol with O-alkyl trichloroacetimidate prepared from allyl alcohol and trichloroacetonitrile is readily accomplished Scheme 4.233]440 as previously discussed for the preparation of benzyl and tert-butyl ethers.311 However, these conditions are not compatible with many of the protecting groups employed in oligosaccharide synthesis. For such cases, two methods for 0-allylation under essentially neutral conditions have been devised. The first method takes advantage of the mild conditions and regioselectivity of stannylene alkylations (see section 4.3.3). The method is illustrated by the selective O-allylation of o-lactal, which began with stannylene formation on an 0.8 mole scale [Scheme 4.234].441... 

Phenols are protected as their methyl ethers ° tert-butyl ethers, allyl ethers and benzyl ethers. 

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