Benzyl Ethers Bn

Related oxidants that have been exploited to similar ends include l-(rm-butoxy)-13-benzoiodoxol-3(l//)-one 2 and sodium bromate. Oxidation of benzyl ethers by l-(/err-butoxy)-13 benzoiodoxol-3(l//)-one followed by easy basic hydrolysis of the resultant benzoate ester provides a convenient alternative to the usual reductive deprotection. The reaction is carried out in the presence of alkali metal carbonates and the conditions are mild enough to be compatible with other hydroxyl protecting groups such as methoxymethyl, tetrahydropyranyk TBS and acetate. 

Oxidative debenzylation using dimethyldioxirane proceeds well with benzyl ethers of primary and secondary alcohols and the method is compatible with silyl ethers. Isopropylidene acetals are stable but benzylidene acetals are cleaved. The deprotection of p-bromo. p-cyano and 2-naphthylmethyl ethers can also be accomplished. 

Our second example again represents the photodeprotection of a 2-nitrobenzyl ether to liberate a phenol in a complex advanced intermediate en route to the putative structure of Diazonamide [ heme 4.158].  

Many sensitive substrates would not survive the ravages of sodium or potassium hydride and the attendant alkoxide anions. There are gentler methods. An alcohol can be protected with benzyl bromide in the presence of silver(I) oxide in 

180 C/0.3 kPa) in refluxing toluene with azeotropic removal of water. A significant impediment to the use of both the stannylene and tributylstannyl ether activation procedures is the generation of large amounts of non-polar tin byproducts that require chromatographic separation. 

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CF3CO2H, PhSCH3, 25°, 3 h. ° The use of dimethyl sulfide or anisole as a cation scavenger was not as effective because of side reactions. Benzyl ethers of serine and threonine were slowly cleaved (30% in 3 h complete cleavage in 30 h). The use of pentamethylbenzene had been shown to increase the rate of deprotection of 0-Bn-tyrosine. ... 

Alkali metals (such as Li) in liquid ammonia are commonly applied for the deprotection of benzyl (Bn) ethers . Lithium naphthalenide prepared from lithium and naphthalene in stoichiometric amount or catalytic amount is often used to deprotect benzyl ethers. 

The PMB ether, also referred to as an MPM ether [(4-methoxyphenyl)methyl], is less stable to acids than a benzyl ether. Its utility as a protecting group stems from the fact that it can be removed oxidatively with DDQ (2,3-dichloro-5,6-dicyano-l,4-benzo-quinone) under conditions that do not affect protecting groups such as acetals, RO-Bn (or RO-BOM), RO-MOM, RO-MEM, RO-THP, RO-TBS, benzoyl, tosyl, or acetate groups, nor do they affect epoxides or ketones. Alternatively, RO-PMB ethers can be cleaved with (NH4)2Ce(N03)6. ... 

Hydrogenolysis catalyzed by Pd/C is widely used to convert benzylic ethers ArCIP-OR to ArCH3 and ROH. The reaction is often accelerated by acid. The simplest possibility for a catalytic cycle is oxidative addition of both H2 and Bn-OR to Pd(0) to give a Pd(IV) complex, followed by reductive elimination of both Bn-H and H-OR to regenerate Pd(0). This mechanism seems very unlikely because the Pd(IV) oxidation state is high in energy. 

The reaction of 1,2 4,5-diketals 49 with a variety of electrophiles has been reported, and it was found that the use of a limited quantity of the reagents and control of reaction temperature may result in a fairly good regioselective monosubstitution at the 3 position. Benzylation of dicyclohexylidene-myo-inositol 49a with benzyl bromide in the presence of NaH under toluene under refluxing conditions was reported to produce selectively the 3-benzyl ether 51 (R=Bn) in 70 (Ref.13a) and 60%27 yields (Scheme 3-2). Benzylation21 28 and allylation-221 using BaO and Ba(OH)2 in DMF afforded successfully the 3-alkylation products 51 (R=Bn and All) in 70 and 68% yields respectively. These authors claimed that combination-27 of BnBr and NaH resulted in poorer selectivity (48%... 

Bn -CH2Ph no (H2 would reduce alkene) yes (benzyl ether stable if pH >1)... 

Fig. 36 Nano-periodic table I Primary dendron structures [S-1] versus 3D supramolecular dendrimer structures [S-l], for all libraries of AB3 supramolecular dendrimers. Bn benzyl ether, Pr phenylpropylether, Bp biphenyl-4-methyl ether, BpPr biphenylpropyl ether [151]. Copyright 2009 American Chemical Society...

O-Isopropylidene-D-mannitol [72] is readily prepared by hydrolysis of 1,2 3,4 5,6-tri-O-isopropylidene-D-mannitol and after alkylation gives the 1,2,5,6-tetra-O-alkylmannitol on acidic hydrolysis and this is readily. converted into l,2-di-0-alkyl-L-glycerol (59). The benzyl (59, R = Bn) [73, 74], allyl (59, R = All) [75] and but-2-enyl (59, R = CH2—CH = CH—Me) [75, 76] ethers have been prepared in this way as intermediates for the synthesis of lipids. 

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