Ethers benzylic, selective cleavage

H2, Pd(OH)2." When the cleavage is performed in dioxane, the DEIPS group is stable and benzyl ethers are selectively removed, whereas if MeOH is use as solvent, both the DEIPS and the benzyl ether are cleaved. 

Conversion of MEM ethers to esters. 2-Methoxyethoxymethyl (MEM) ethers are converted into carboxylic esters by reaction with an anhydride in the presence of FeCl3 (0.4 equiv.) (equation I). Selective cleavage is possible in the presence of a benzyl ether but not in the presence of a f-butyl ether. Aromatic rings, if present, can undergo acylation. 

The cleavage of benzyl ethers using hydrobromic acid is promoted by tetra-n-butylammonium bromide [38]. Selective cleavage of aryl silyl ethers can be effected in the presence of aliphatic silyl ethers using solid sodium hydroxide with tetra-n-butyl-ammonium hydrogen sulphate [39]. 

Potential-selective cleavage is a powerful method for potential-selective deprotection. Benzyl ethers can be cleaved to benzaldehyde and alcohol via oxidation of the benzyl group to a radical cation (Fig. 30) [148]. With the radical cation of... 

Bromotrimethylsilane has proven to be useful for a wide variety of applications most of them being reviewed.5 8 Other recent applications are mild cleavage of oxiranes,9 the synthesis of glycosyl bromides,10 the selective cleavage of tetrahydro-2,5-dimethoxyfuran and tetrahydro-2,6-dimethoxy-pyran,11 the cleavage of esters and ethers,12 and the synthesis of benzyl bromides.13... 

Selective cleavage of aryI methyl ethers.1 The sodium salt (NaH) of N-melhylaniline in the presence of HMPT cleaves methyl (and benzyl) aryl ethers in... 

In contrast to the reaction of y-stannyl alcohol 50, the y-stannyl benzyl ether 53 results in selective cleavage of the butyl-tin bond by reaction with (PhIO)n 18/DCC/BF3 and, after quenching of the reaction mixture with aqueous NH4C1, afforded the chlorostannane in high yield. Interestingly, the chlorostannane both in solution and in the solid state adopts a 1,3-diaxial conformation through Sn-O hypervalent interaction [82]. 

N-Salicylideneamines, to protect amines, 370 Selective cleavage, 411-412 of benzyl carbamates, 339-340 of benzyl ethers, 49-56 of catechol protective groups, 171 of N- vs. 5-dimethylphosphinothioyl groups, 307... 

Protection of the peripheral phenolic groups as benzyl ethers was selected so that regioselective cleavage of these ethers in the presence of interior aliphatic ether linkages could be effected to liberate phenolic groups at some later stage. These functionalized dendrons were coupled to various anchor cores to produce... 

Cleavage of MEM ethers. 2-Methoxyethoxymethyl (MEM) ethers are cleaved by NaI/ClSi(CH,)3 in CHjCN at —20 or 25° in moderate to high yield, lodotrimethylsilane (commercial) is less effective. Fairly selective cleavage of MEM ethers is possible in the presence of lactones, methyl or benzyl ethers, and methyl esters. 

Hwu and co-workers reported selective cleavage of a benzyl (Bn) ether with lithium di-isopropylamide (LDA) in the presence of a methoxy group however, by using sodium bis(trimethylsilyl)amide [NaN(SiMe3)2], the dimethoxybenzene undergoes selectively mono-O-demethylation (Scheme 1.21). 

Acidolysis causes the selective cleavage of arylglycerol-)6-aryl ethers (4, Fig. 6.1.2) and some other types of labile ether linkages, and this has been utilized on several occasions, for example by Kirk and Adler (1970). Treatment with the acidolysis reagent at 50°C (Adler et al. 1968) has been used in lignin chemistry for the selective hydrolysis of noncyclic benzyl aryl ethers. 

Aryl benzyl ethers are cleaved more easily than are alkyl benzyl ethers. The presence of an amine hinders the hydrogenolysis of alkyl benzyl ethers but has no effect on the cleavage of aryl benzyl ethers. - Because of this the benzyl ether is selectively hydrogenolyzed in compounds containing both a benzyl amine and an aryl benzyl ether (Eqn. 20.24)55 but the benzyl amine is selectively cleaved in compounds having both a benzyl amine and an alkyl benzyl ether (Eqn. 20.25).53,54,56... 

Since the reaction with the [(benzyloxy)(benzyloxycarbonyl)methyl] trimethylphosphonium ylide 92 was quite successful, it was also used to couple the isomeric D-altro-, D-ido-, D-talo-, and D-gulo-per-O-benzylated aldehydes [94b]. Transesterification of the products with methanol gave exclusively Z-isomers in all of the cases. Debenzylation enabled the selective cleavage of the enol ether functions. Subsequent... 

Cleavage of propargyl ethers. With the low-valent Ti species (from TiCla, Mg in THF) the reductive cleavage of propargyl ethers is selective, since allyl, benzyl, and methyl ethers remain intact under these conditions. 

Selective cleavage, so often a prerequisite in synthesis, of an aryl benzyl ether was effected in 80% yield with the dibenzyl ether of estrane-3,17-diol in chloroform containing N,N-dimethylaniline by the addition of powdered aluminium chloride, stirring during 30 mins, at ambient temperature, and work-up following quenching with M hydrochloric acid (ref.95). 

Debenzylation. MgBr2 effects a selective cleavage of benzyl ethers of o-hydroxy phenones. 

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