P-Nitrobenzyl ether

The o-nitrobenzyl and p-nitrobenzyl ethers can b prepared and cleaved by many of the methods described for benzyl ethers. The p-nitrobenzyl ether is also prepared from an alcohol and p-nitrobenzyl alcohol (trifluoroacetic anhydride, 2,6-lutidine, CH2CI2, 67% yield). In addition, the o-nitrobenzyl ether can be cleaved by irradiation (320 nm, 10 min, quant, yield of carbohydrate " 280 nm, 95% yield of nucleotide ). The p-nitrobenzyl ether has been cleaved by electrolytic reduction (—1.1 V, DMF, R4N X, 60% yield) and by reduction with Na2S204 (pH 8-9, 80-95% yield). These ethers can also be cleaved oxidatively (DDQ or electrolysis) after reduction to the aniline derivative. ... 

The o nitrobenzyl and /7 nitrobenzyl ethers can be prepared and cleaved by many of the methods described for benzyl ethers. The p-nitrobenzyl ether is also... 

For a time, considerable attention was focussed on stereoisomeric changes about the C=N double bond in substituted benz-syn-aldoximes, e.g., the partial isomerization of methyl ethers of m-and p-nitrobenz-spn-aldoximes and the complete conversion of the a-O-p-nitrobenzyl ethers of o-, m-, and p-aldoximes.26 In the case of the semicarbazones, the isomeric changes can be attributed to tautomerism in the urea portion of the molecule without the necessity of considering stereisom-erism about the double bonds in other portions of the molecule.266,310... 

Problem 17.6 Outline the synthesis of phenyl p-nitrobenzyl ether from any of these starting materials toluene, bromobenzenc, phenol. (Caution Double-check the nitration stage.)... 

The p-nitrobenzyl ether is also prepared from an alcohol and p-nitrobenzyl alcohol (trifluoroacetic anhydride, 2,64utidine, CH2CI2, 67% yield) or with the bromide and Ag20." ... 

Cleavage is generally accomplished by first reducing the nitro group and then removing the p-aminobenzyl ether with acid or oxidatively with DDQ." Thus, conditions that reduce a nitro group should be applicable for the deprotection of this ether. Some of the methods that have been used specifically for the p-nitrobenzyl ether are as follows. 

The strategy eluded to in Scheme 7.3.7 is elaborated upon in Scheme 8.10.5 and involved the starting material prepared in Scheme 8.10.3. Cyclization of the polyol is effected on removal of the acetonide under acidic conditions followed by the oxidative cleavage of the resulting diol. Spontaneous formation of the hemiacetal is followed by protection as the p-nitrobenzyl ether. Although two diastereomers are formed in this sequence, the minor product is easily converted to the major under mild basic hydrolysis of the p-nitrobenzyl ether followed by reprotection of the isomerized hemiacetal. This compound is then converted to the allene, shown, on treatment with propargyltrimethylsilane in the presence of trimethylsilyl triflate. 

Reductions. Reports of rather simple reductions by indium keep appearing of tx-halocarbonyl compounds in water with ultrasound assistance, of p-nitrobenzyl ethers and esters, disulfides, amine IV-oxides, and organic azides in alcoholic solvents in the presence of NH4CI. When the azide reduction is carried out in DMF the products can be directly converted to carbamates by having a chloroformate ester in the reaction vessel. ... 

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