P-methoxybenzylidene

The p-methoxybenzylidene acetal is a versatile protective group for diols tl undergoes acid hydrolysis 10 times faster than the benzylidene group. ... 

The p-methoxybenzylidene ketal can be prepared by DDQ oxidation of a methoxybenzyl group that has a neighboring hydroxyl. This methodolc... 

The p-methoxybenzylidene ketal can be prepared by DDQ oxidation of a p-methoxybenzyl group that has a neighboring hydroxyl. This methodology has been used to advantage in a number of syntheses. " In one case, to prevent an unwanted acid-catalyzed acetal isomerization, it was necessary to recrystallize the DDQ and use molecular sieves. The following examples serve to illustrate the reaction " ... 

Acetonide Derivative 11. Benzylidene Acetal 13. p-Methoxybenzylidene Acetal 18. Methoxymethylene Acetal 20. Dimethoxymethylenedioxy Derivative... 

The IAD concept via p-methoxybenzylidene acetals was also shown to be suitable for polymer-supported syntheses of disaccharides (Scheme 5.107) [292], A suitable p-allyloxybenzyl group at position 2 of a 1-thio-mannosyl donor is first converted into a PEG-modified benzyl group that allows for the convenient isolation of the intermediate tethered glycosides. 

The synthesis of (3-D-fructofuranosides is yet another useful application of this concept [293-295]. The latter 1,2-cis-glycosidic linkage is as difficult to establish as in the case of (3-mannosides. In an elegant synthesis of a-D-fucofuranose-containing disaccharides, Plusquellec and coworkers used the IAD concept via p-methoxybenzylidene acetals in combination with a glycosylation protocol via pentenyl glycosides. Here, the intermediate NIS-adduct could be isolated (Scheme 5.108) [295]. 

Dan, A. Lergenmuller, M. Amano, M. Nakahara, Y. Ogawa, T. Ito, Y., p-Methoxybenzylidene-tethered beta-mannosylation for stereoselective synthesis of asparagine-linked glycan chains. Chem. Eur. J. 1998,4, 2182-2190. 

The anodic oxidation of a number of 1-arylmethylenesemicarbazides (60) has been studied in CH3CN-AcOH containing sulfuric acid.118 This method provides a convenient preparative route to either oxadiazole (61) or triazoli-none (62) derivatives. The reactions were very sensitive to the concentration of water and under ordinary conditions the oxadiazole (61) is formed in 85% yield by oxidation of l-(p-methoxybenzylidene)semicarbazide. By addition of acetic anhydride, in order to reduce the water content, the triazolinone derivative 62 was formed in 45% yield [Eq. (50)]. 

The use of a Lewis acid (e.g., friethylfluoroborate, zinc chloride, stannous chloride, titanium chloride, iron(m)chloride) and other reagents (e.g., iodine, trimethylsilane, trifluoiomethane-sulfonylsilane) have also been recommended. Exhaustive lists of catalysts and conditions can be found in reviews devoted to carbohydrates [5-7], or to general organic chemistry [27,28], However, one can add the new catalyst, which has been introduced for the smooth formation of p-methoxybenzylidene acetals and p-methaxy-phenylmethyl methyl ether [29], namely 2,3-dichloro-5,6-dicyano-p-benzoquinone (DDQ), and has been applied very recently [30] to the synthesis of isopropylidene mixed acetals. 

Reductive cleavage, using the NaCNBHj-HCl-THF system to produce 2 -pro-penylidene acetals, produced the same regioselectivity as that found in benzylidene acetals [27] (Scheme 11), and also for the p-methoxybenzylidene acetals (Scheme 12) [27]. These observations open the way to further strategies for protecting group manipulations. 

Glasses have also been reported for nematic p-methoxybenzylidene-p-n-butyl-aniline 66) and some commercial liquid crystals 67) and for smectic ethyl-(p-anisol-amino)-cinnamate 68), p-n-hexyloxybenzylidene-p-aminobenzoic acid (Tg = 376 K) and p-n-nonyloxybenzylidene-p-aminobenzoic acid (Tg = 203 K) 69). 

Sorai, M. and Seki, S. Glassy liquid crystal of the the nematic phase of N-(o-Hydroxy-p-methoxybenzylidene)-p-butylaniline. Bull. Chem. Soc. Japan 44, 2887 (1971)... 

Due to the neutral and very mild conditions used in TPAP oxidations, virtually all protecting groups remain unaffected, including the very oxidant-sensitive PMB ethers77 and p-methoxybenzylidene acetals 78 and the very acid-sensitive TMS ethers.76... 

Name 4,4 -Bis-(p-methoxybenzylidene amino)-3,3 -dichloro biphenyl Structure ... 

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