Dibenzyl ether, substituted

When (3-substituted phenyl)aminomethylenemaIonate (1163, 3-R = H) was applied, a mixture of 5-substituted and 7-substituted 4-hydroxyquino-lines (1164, 5-R + H and 7-R + H) was obtained. For example, the thermal cyclization of (3-nitrophenyl)aminomethylenemalonate in dibenzyl ether at 250°C afforded a 3 1 mixture of 7-nitro- and 5-nitro-4-hydroxy-quinolines (1164, R = 7-N02 and 5-NO ). 4-Hydroxyquinolines (1164) could also be prepared when a mixture of anilines, triethyl orthoformate, and isopropylidene malonate was slowly heated to 100°C in Dowtherm A, stirred over a period of 30 minutes, and then raised to a temperature of... 

Among the 1,4-di-O-substituted-L-threitol derivatives (Figure 14a) the one that has found most use in chiral crown ether synthesis is the 1,4-dibenzyl ether. Not only has it provided (88, 106, 107) a ready entry into the chiral tetrasub-stituted 18-crown-6 derivatives ll-31 to ll-34, but it has also proved to be a usehil chiral precursor for the preparation of chiral disubstituted 9-crown-3 (107), 12-crown-4 (108), 15-crown-5 (108), and 18-crown-6 (109) derivatives l-57, l-58, l-59, and l-60, respectively. In the preparation of l-S8 the base-promoted cyclization with triethylene glycol ditosylate is best carried out (108) with a... 

A number of substrates having a benzylic ether moiety were reacted with 51 to afford the corresponding benzylic esters in good yields (equation 84)238. For evaluating the effects of p-substituents on the oxidation of a series of benzylic ethers, a competitive oxidation of p-substituted benzylic propyl ethers with 51 was carried out. The Hammett correlation plot for the oxidation reaction gave a better correlation of the relative ratio factors with the a rather than with the o+ substituent constants and afforded a reaction constant p+ = —0.57 (r = 0.99). This p+ value shows that 51 is an electrophilic species and appears to be comparable to the p+ value of —0.65 for benzylic hydrogen abstraction from dibenzyl ethers by the benzoyloxy radical239. 

Olah and co-workers219 have applied Nafion-H in the benzylation of benzene with benzyl alcohols [Eq. (5.83)] and also reported the reaction of benzyl alcohol with substituted aromatics (toluene, xylenes, mesitylene) to yield diphenylmethanes. The reaction is performed under mild conditions and produces the corresponding dibenzyl ethers as byproducts (2-22%). The substrate and positional selectivity in competitive benzylation of benzene and toluene (1 1 molar ratio) was found to be almost the same as observed in solution-phase Friedel-Crafts benzylation with benzyl chloride (AICI3-CH3NO2). Cyclic products 56 and 57 resulting from cyclialkylation were isolated when Nafion-H-catalyzed benzylation was applied to 2-(hydroxymethyl) diphenylmethane and 3,4-dimethoxybenzyl alcohol, respectively. 

Methyl 2,3-isopropylidene-a-L-rhamnopyranoside was converted into the 4-tosyl derivative (LVII), from which the isopropylidene residue was removed by mild hydrolysis. Methylation then gave methyl 2,3-di-methyl-4-tosyl-a-L-rhamnopyranoside (LVIII), from which the reductive fission of the aromatic residue with sodium amalgam followed by hydrolysis gave 2,3-dimethyl-L-rhamnose (LIX).68 The same product was obtained by the substitution of benzoyl for tosyl, followed by methylation and separation on a column of cellulose.84 In an earlier synthesis,89 2,3-isopropylidene-L-rhamnose was converted into the 1,5-dibenzyl ether (LX) by treatment with benzyl chloride and potassium hydroxide. 

When the aryl ring is activated towards electrophilic attack as in diphenylamine, trichlorophosphine is able to substitute at the ortho position and, at 200 °C, ultimately produce the spirophos-phonium salt (13) <7ICCI213>. If the forming bond to phosphorus is from a heteroatom, a P(III) phosphorus can be made electrophilic. Such an example is the the cyclization of the dibenzyl ether (122) to give phosphorane (42 Y, Z = CH2, R = Ph) as shown in Scheme 5 <82JCS(P1)735>. 

Gustowski, D. A., Gatto, V. J., Mallen, J., Echegoyen, L., Gokel, G. W., Direct correlation of cation binding strengths to Hammett parameters in substituted TV-benzylaza-15-crown-5 lariat ether and A 7V-dibenzyl-4,13-diaza-18-crown-6 BiBLE derivatives. J. Am. Chem. Soc. 1987, 52, 5172-5176. 

Diazetidines and/or oxadiazines are obtained from cnol ethers and acyclic diacyldiazenes depending on the structure and the substitution pattern of the alkene (Section 7.2.10.1.). For 3,4-dihydro-2//-pyran (12) and certain glycals it has been found that the cycloaddition of dibenzyl di-azenedicarboxylate 13 to give oxadiazines is favored over the ene products by carrying out the reactions at lower concentration of dihydropyran and under irradiation, which converts ( )-13 to (Z)-1312. 

This compound displays a slightly pyramidal geometry at the a-carbons, and the phenyl rings are not coplanar, which is typical for sterically congested multiphenyl-substituted ligands of this type. The increased steric demand of the ligand together with the electronic and coordinative stabilization provided by the crown ether enable increased stability as compared to the dibenzyl derivative. Remarkably, crown ether-stabilized barium diphenylmethanide is sufficiently stable to allow for recrystallization from hot THF, whereas dibenzylbarium reacts readily with THF at temperature above -40 °C. 

Stereoselective reactions with acetals. Noyori et al. (10,438) have used this Lewis acid to promote an aldol-type reaction between enol silyl ethers and acetals and have noted high. syn-selectivity in this process. Molander and Haar report that reaction of acetals with cyanotrimethylsilane promoted by TMSOTf results in a-alkoxy cyanides and that this reaction can be diastereoselective when the acetal is substituted at the 4-position by an alkoxy group. The diastereoselectivity depends on the nature of the acetal and the 4-alkoxy group. Dimethoxy acetals show slight diastereoselectivity, but diisopropoxy and dibenzyl acetals can show diastereoselectivity of 5-10 1. The diastereoselectivity also depends on the type of 4-substituent. Acetoxy and t-butyldimethylsilyloxy groups have no effect on the diastereoselectivity, but methoxy, benzyloxy, and allyloxy groups promote anri-selectivity. Since a metal template is not involved, the diastereoselectivity... 

The latter is known as the elimination-addition mechanism of the nucleophilic aromatic substitution. The high reactivity of aryllithiums precludes the use of several types of functional groups such as aldehydes, ketones, esters, amides, amines, alcohols, phenols, nitro-compounds, carboxylic acids etc. However, properly protected alcohols, phenols or amines can effect the reaction. Various ether protecting groups, e.g. Tr, Me, /-Pr, Bn, 4-MeOBn, are employed in the former instances, whereas A, V-dibenzyl group is convenient for the amine protection. 

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