P-methoxy benzyl

Quinoxalin-2-ones are in tautomeric equilibrium with 2-hydroxy-quinoxalines, but physical measurements indicate that both in solution and in the solid state they exist as cyclic amides rather than as hydroxy compounds. Thus quinoxalin-2-one and its A -methyl derivative show practically identical ultraviolet absorption and are bases of similar strength. In contrast, the ultraviolet spectra of quinoxalin-2-one and its 0-methyl derivative (2-methoxyquinoxaIine) are dissimilar. The methoxy compound is also a significantly stronger base (Table II). Similar relationships also exist between the ultraviolet absorption and ionization properties of 3-methylquinoxalin-2-one and its N- and 0-methyl derivatives. The infrared spectrum of 3- (p-methoxy-benzyl)quinoxalin-2-one (77) in methylene chloride shows bands at 3375 and 1565 cm" which are absent in the spectrum of the deuterated... 

Zimmerman and co-workers<135> have reported that photolysis of p-methoxy-benzyl acetate in aqueous dioxane results in p,p -dimethoxybibenzyl and bidioxane, probably through the intermediacy ofp-methoxybenzyl radicals ... 

M Fujino, O Nishimura. A new method for the cleavage of S-p-methoxy-benzyl and 5-t-butyl groups of cysteine residues with mercury(II) trifluoroacetate. J Chem Soc Chem Commun 998, 1976. 

In an extension of this work, Schnider and his colleagues condensed the salt (36) with the Grignard reagent from p-methoxy-benzyl chloride. The product (40), on reduction (41) and cyclizar-tion, affords the methoxylated morphinan (41). Removal of the methyl ether affords the narcotic analgesic racemorphan (43). ... 

During the reaction of p-methoxy benzyl alcohol with silyl enol ether 31b, dibenzyl ether 33 was observed as a by-product, which disappeared after prolonged reaction time. In fact, if 33 was used as alkylating reagent, the silyl enol ether 31b was benzylated and the desired cyclopentanone 32e was obtained in a similar yield (Scheme 25). 

Chemoselective catalytic hydrogenolysis (10 % Pd/C) of the glycosidic benzyl group of a 2-amino-2-deoxy-D-glucosederivative that carries another benzyl group protecting a 3-hydroxytetradecanoyl substituent at 0-3 has been applied in an efficient synthesis of lipid Y [215]. Benzyl ether is cleaved selectively in the presence of p-methoxy-benzyl ether by Raney nickel hydrogenolysis [216]. 

Also 2 -halo-3 -hydroxy derivatives of various anthracyclinones show a high activity against P 388 mouse leukemia in certain in-vivo tests. A compound like 98 has been prepared in the 2-deoxy-2-iodo-a-L-ma no-series by Horton et al. [59, 60] starting from di-O-acetyl-L-rhamnal (28). Similarly, Thiem et al. have also successfully prepared the tetracenomycinone-C glycoside 99 [61]. From 4-0-acetyl-3-0-(p-methoxy)-benzyl-L-fucal (102) the glycoside derivatives 103 and 104 in the talo-series were obtained. 

The position of the substituents on the pyridine moiety also affects the activity of the initiator. For example, p-MeO benzyl o-CN pyridinium salt 2k is 100 times more reactive than the corresponding p-CN derivative 2f. Thus, introduction of the o-cyano group into pyridine nucleo causes a large enhancement of the initiator activity. The reason for the activity enhancement by this modification can be accounted for by both electronic and steric effects of the o-cyano group of the pyridine group. In a typical comparison of the initiation activities of p-CN 2f and m-COOMe 21 substituted p-methoxy benzyl pyridinium salts in the polymerization of GPE, it was observed that p-substituted salt 2f is approximately 10 times more reactive than the corresponding o-substituted salt 21. In this case the steric effect of the substituents is negligible. A similar... 

Creation of the 8-membered ring 3 3 of IhxoL by an intramolecular directed aldol reaction failed when the thionium ion intermediate 3 2 underwent intramolecular hydride transfer from a neighbouring p-methoxy benzyl ether instead [Scheme 1.38]. Loss of p-methoxybenzaldehyde and hydrolysis of the enol silane occurred on workup to give the hemiacetal 38,5 in 48% yield. Benzyl ethers can also transfer hydride to proximate carbocationic intermediates.71... 

Diisobutylalane is both a Lewis acid and a reducing agent that selectively cleaves arylmethylene acetals. The reaction conditions are compatible with the presence of fm-butyldiphenylsilyl ethers [Scheme 3.63]106 and p-methoxy benzyl ethers [Scheme 3.64].107 108 The high regioselectivity in the latter case is at first surprising but an X-ray structure of the substrate shows that the bond selectively cleaved is longer in the ground state and therefore weaker. 

Protic acids will also cleave p-methoxy benzyl ethers under comparatively mild conditions. At 90 cC, acetic acid is sufficient352 but the reaction works at room temperature with as little as 0.5% trifluoroacetic acid in dichloromethane.353 p-Methoxybenzyl groups can be removed selectively with trifluoroacetic acid in the presence of secondary glycosidic linkages, azides, or phenylthio glycosides [Scheme 4.189],354 The survival of a trisaccharide under the deprotection conditions indicates that p-methoxybenzyl groups may be useful in oligosaccharide synthesis. 

The sodium alkoxides prepared from primary and secondary alcohols and sodium hydride in a mixture of THF and DMF or DMSO react with p-methoxy-benzyl chloride at room temperature to give the p-methoxybenzyl ethers in good yield. Use of THF alone is not so satisfactory. p-Methoxybenzyl chloride (nip -1 °C bp 117 C/L9 kPa) is moisture sensitive and deteriorates on standing so it should be freshly distilled in vacuo before use. In sluggish reactions, the rate can be increased by the addition of a catalytic amount of tetrabutylam-... 

Peptide chemists usually come from the eupeptic end of the scale of human felicity but anyone who performs the deprotection of a benzyl ester with 33% hydrogen bromide in acetic acid could be accused of brutality. That peptides survive is more a tribute to the molecules than the chemists who make them. The method is illustrated in Scheme 6.39.97 The reactivity of the benzyl ester can be augmented by adding a methoxy group to the para position. p-Methoxy-benzyl esters will cleave with trifluoroacetic acid in anisole or with a catalytic amount of trifluoroacetic acid in a phenol matrix at 45 °C.70... 

A synthesis of (-)-Chlorothricolide was impeded by problems deprotecting the spirotetronate unit in 63 1 [Scheme 6.63].159 Early attempts to deploy 2-(tri-methylsilyl)ethoxymethyl or p-methoxy benzyl ethers failed because the product was unstable to the conditions of the deprotection. After much experimentation, a solution to the problem was found simultaneous deprotection of the spirotetronate and the carboxyl group was achieved with Pd(0) and dimedone in 94% yield. 

Cbz Cp DABCO DBU DDQ (DHQD)2CLB (DHQD)2PYR DMF DME DMPU DMSO Et Fmoc HMPA ia KHMDS LDA LiHMDS Me MEM Ms NaHMDS Ph Piv PMB Pr Py (saltmen)Mn(N) benzyloxy carbonyl p 5 -cyclopentadienyl l,4-diazabicyclo[2.2.2]octane l,8-diazabicyclo[5.4.0]undec-7-ene 2,3 -dichloro-5,6-dicyanobenzoquinone dihydroquinidinyl p-chlorobenzoale (see Chart 1) dihydroquinidinyl pyrimidine (see Chart 1) dimethylformamide dimethoxyethane l,3-dimethyl-3,4,5,6-tetrahydro-2(l//)-pyrimidinone dimethylsulfoxide ethyl 9-fluorenylmethoxy carbonyl hexamethylphosphoric triamide inverse addition potassium hexamethyldisilazide lithium diisopropylamide lithium hexamethyldisilazide methyl (2-methoxy ethoxy )methyl methanesulfonyl sodium hexamethyldisilazide phenyl pivaloyl p -methoxy benzyl propyl pyridine nitrido[A,A/-(l,l,2,2-tetramethyl) bis(salicylideneaminato)]manganese (see Chart 1)... 

The core structure 63 of azinomycins A and B has been synthesized from the 1,1-bis(ethylthio)-4,6-isopropylidene D-arabinose derivative 54 by treatment with p-methoxy-benzyl chloride, followed by removal of the dithioacetal groups with N -bromosuccinimide and subsequent reduction of the resulting aldehyde to afford 55 (Schemes 7 and... 

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