2-Nitrobenzylidene derivatives

The conversion of benzylidene and ethylidene derivatives into hydroxy benzoates and hydroxy acetates, respectively, following irradiation in acetone, and preferably in the presence of oxygen, was discussed by Binkley. Irradiation is carried out at a shorter wavelength (compared to 2-nitrobenzylidene derivatives) and the yields are significantly lower. 

The benzylidene or Tw-nitrobenzylidene derivatives, because of their insolubility, are well suited for isolation of small quantities of hexitols. The difficulty in obtaining completely or partially benzylidenated products free from one another limits their usefulness for characterization, since varying melting points are obtained. Cia-trans isomerization is another complication. Conversion to the acetates obviates these difficulties. 

The diketothienothiophene (249b) can be condensed with aldehydes thus p-nitrobenzaldehyde gives the 2,5-bis-p-nitrobenzylidene derivative (250). ... 

This reaction was extended to 0-(o-nitrobenzylidene) derivatives of glycerol,67 D-mannitol,68 and D-glucitol.69 Some regioselectivity seems to have been observed, as two acetal groups [of the three for the tri-O-(o-nitrobenzylidene) derivatives of D-mannitol and D-glucitol] were found to have reacted. The identity and the structure of the photo-... 

The N-methyl derivatives of 1 -aryl-1,4-dihydro-3(2//)-isoquinolinones (e.g., 54) can be lithiated in position 4 with butyllithium. The subsequent reaction, e.g., with p-nitrobenzaldehyde, gives the 4-p-nitrobenzylidene derivative. In this case, the condensation reaction is not followed by H-l rearrangement [86ACH(121)263]. 

Tanasescu and his co-workers88-70 have shown that o-nitrobenzylidene acetals, in chloroform or benzene solution, undergo photochemical transformations when exposed to sunlight. It appears that, under these conditions, an o-nitrobenzylidene derivative (III) may be converted into an isomeric o-nitrosobenzoy lester (IV). Thus, Tanasescu and Macov-ski86 showed that a di-(o-nitrobenzylidene)-dibenzoyl-dulcitol, later shown to be 1,3 4,6-di-(o-nitrobenzylidene)-2,5-dibenzoyl-dulcitol,48 could... 

Scheme II.—Utilization of a 2-Nitrobenzylidene Protecting Group in the Synthesis of Methyl 6-Deoxy-2,3-di-0-/3-D-galactopyranosyl-a-L-galactopyranoside. /3-o-GaIacto-pyranosyl (R ) Substituents Were Introduced by Koenigs-Knorr Syntheses, and the Photochemical Cleavage, at 350 nm, of the 2-Nitrobenzylidene Groups Proceeded Regiospecifi-cally. Yielding, Following Oxidation, a 95% Yield of the 3-Hydroxy-4-(2-nitrobenzoate) Derivative.

Groups of reportedly photochromic systems which deserve further study include (a) disulfoxides (123,124), (b) hydrazones (125-129), (c) osazones (130-133), (d ) semicarbazones (134-143), (e) stilbene derivatives (144), (/) succinic anhydrides (145-148), and (g) various dyes (149,150). A number of individual compounds also remain unclassified as to their mechanism of photochromic activity. These include o-nitro-benzylidine isonicotinic acid hydrazide (151), 2,3-epoxy-2-ethyl-3-phenyl-1-indanone (152), p-diethyl- and p-dimethyl-aminophenyli-minocamphor (153), brucine salts of bromo- and chloro-nitromethionic acid (154), diphenacyldiphenylmethane (155,156), 2,4,4,6-tetraphenyl-1,4,-dihydropyridine (155,156), 2,4,4,6-3,5-dibenzoyltetrahydropyran (155,156), o-nitrobenzylidenedesoxybenzoin (157), p-nitrobenzylidene-desoxybenzoin (157), N-(3-pyridyl)sydnone (158,159), tetrabenzoyl-ethylene (160), and the oxidation product of 2,4,5-triphenylimidazole (161,162). 

Three monoacetals, o-,70 wi-97 and p-nitrobenzylidene-dulcitol,97 have been described, the first being formulated, without proof, as the 3,4-derivative. The only triacetal of dulcitol of which we are aware is a tri-(o-nitrobenzylidene)-dulcitol prepared from the aldehyde and the hexitol using as the condensing agent phosphorus pentoxide,70 instead of 75% sulfuric acid which gives the diacetal already mentioned.48 6 Photochemical transformations of o-nitrobenzylidene acetals are discussed on page 148. 

Anodic oxidation of substituted hydrazones may induce ring closure. Oxidation of /7flrfl-substituted phenylhydrazones of 2-oxophenylacetonitrile yields derivatives of 1-phenyl-3-cyano-l/7-indazoles [73] p-nitrobenzylidene-o-phenylenediamine is oxidized in MeCN-LiC104 to 2-(pnitrophenyl)benzimidazole [74], chalchone phenylhydrazone in MeCN-C5H5N-LiC104 to 1,3,5-triphenylpyrazol [74], and benzylidene 2-pyridylhydra-zone (XXIV) to 3-phenyl-j -triazolo[4,3-a]pyridine (XXV) oxazoles and imidazoles may be prepared similarly [74] ... 

Complementary to their studies on the 0-nitrobenzylidene acetals of alditols, Tanasescu and coworkers prepared some corresponding derivatives of aldoses and examined their properties on irradiation with ultraviolet light. They found that the di-0-(o-nitrobenzylidene)aldoses are converted into 1,2-0-(o-nitrobenzylidene)-3-0-nitrosobenzoyl derivatives. In a later paper, the formation of optically inactive products from this treatment was described, but the structure of these compounds needs elaborating. These phenomena may be of greater value in effecting transformations in the carbohydrate series when more is known about them. 

It is usual to start with a nitrated toluene and convert this into the iV-(nitrobenzylidene)-aniline, which is easily hydrolysed by concentrated hydrochloric acid to the nitro aldehyde and the amine. Toluenes are converted into benzylideneanilines either by treatment of the derived benzyl halide with aniline, followed by oxidation with potassium permanganate,203 or by condensation of nitrotoluenes with N,N-dimethy 1-p-nitrosoaniline205-208 as first described by Sachs.204 It should be specially noted that the condensation product of 2,4,6-trinitrotoluene with A N-dimethyl-p-nitrosoaniline has a strong tendency to explode.206 For similar compounds see also pages 447-448. 

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