Benzyl ethers, cleavage selective

Cleavage of benzyl ethers. Selectivity is observed, as exemplified in the following. ... 

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. 

The selective and facile cleavage of the benzylic ether linkages of 1,2,3 or 4 is accomplished by treatment with iodotrimethylsilane to form the corresponding benzylic iodide. Further addition to these iodide derivatives of 1 affords dendrimers of generation 1 with phosphonium ion sites at the periphery. Such a strategy is conducted up to generation 3 with a phosphine or a phosphonium core (Scheme 3). 

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... 

Since 1995, Tietze et al. [26-32] have studied the use of norpseudoephedrin derivative 61 as a chiral auxiliary in order to perform a diastereocontrolled SMS reaction. Further cleavage of the benzylic ether bond of 62 by Na/NH3 led to optically active homoallylic alcohol 26 with good yields and selectivity (Scheme 13.25). 

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]. 

Regioselective debenzylation can be achieved by treatment with Lewis acids such as ferric chloride and S11CI4 or under acetolysis conditions with acetic anhydride and sulfuric acid, and several examples are depicted in Scheme 2.3.9 Acetolysis results in cleavage of the most acid-sensitive benzyl group. In general, primary benzyl ethers can be selectively acetolysed in the presence of secondary benzyl ethers. The regioselectivity of the reaction can be explained as follows sulfuric acid protonates acetic anhydride followed by the formation of an acetyl ion and acetic acid. The acetyl ion reacts with the sterically most accessible oxygen which is at... 

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... 

The regiochemistry of reductive cleavage of p-methoxybenzylidene acetals depends on the substrate and the reaction conditions. By suitable choice of solvent and electrophile, the distribution of regioisomers can be controlled in some cases. For example, sodium cyanoborohydride cleaved glucose derivative 66.1 [Scheme 3.66] selectively to the 6-0-p-methoxybenzyl ether 663 using trifluoro-acetic add as electrophile and DMF as solvent whereas the 4-Op-methoxy-benzyl ether 663 predominated when chlorotrimethylsilane was used as electrophile in acetonitrile as solvent.115 Note, however, that application of the latter conditions to the p-methoxybenzylidene acetal 67,1 [Scheme 3.67] gave the p-methoxybenzyl ether of the less hindered primary hydroxyl as well as rearrangement of the isopropylidene acetal,116... 

---