O-Nitrobenzaldehyde Acetals

The substitutions by o-nitrobenzyl groups are used for dioxolane and 1,3-dioxane derivatives, but the photochemical cleavage is only partially regioselective. However, 

Resistant to acids and bases and without a tendency to migrate, this group is stable for all the reactions employed in the synthesis of oligonucleotides. It is photolytically cleaved under a controlled pH without affecting the pyrimidine or purine bases [107, 108]. It has also been used as a photoremovable protecting group for the phosphate function [109]. 

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C.C. Petropoulos, Synthesis of novel photodegradable poly(o nitrobenzaldehyde acetal) poly mers, J. Polym. Set, Polym. Chem. Ed. 15, 1637 (1977). 

An old and satisfactory method is the Riedel synthesis in which o-nitrobenzaldehyde is converted to its bisformaraido derivative followed by reductive cyclization with zinc and acetic acid, or with iron and hydrochloric acid. This synthesis has been used to make... 

Cyclic acetals derived from diols and o-nitrobenzaldehyde produce hydroxynitrosobenzoates upon irradiation (see Scheme 26). Early studies of this reaction demonstrated that acetals involving carbohydrates and o-nitrobenzaldehyde experience facile, photochemical... 

In this process o-nitrobenzaldehyde is condensed in alkaline solution with acetone. The so-called o-nitrophenyUactic acid ketone thus formed loses acetic acid, and by further loss of a molecule of water is changed into indolone, which corresponds to half of the indigo molecule. Possibly o-nitrostyrene is an intermediate stage in this transformation. Indolone cannot exist in the free state, and hence polymerises at once to the dye ... 

Cohare and co-workers reported that aristolactam BU (22) was prepared, following Kupchen s method, by Perkin condensation of 6-bromo-3,4-di-methoxy phenyl acetic acid (119) and o-nitrobenzaldehyde (120) (Scheme 14). The 2-bromo-4,5-dimethoxy-2 -nitro-ds-stilbene-a-carboxylic acid (121) was obtained. The nitro group of 121 was reduced with ferrous sulfate and ammonium hydroxide, and the resulting 2-bromo-4,5-dimethoxy-2 -amino-cw-stilbene-a-carboxylic acid (122) without purification was submitted to the Pschorr phenanthrene synthesis to yield l-bromo-3,4-dimethoxyphen-anthrene-lO-carboxylic acid (123). The phenanthrylamine 124 was prepared from 123 via a Schmidt reaction, and, by treatment with n-butyllithium and CO2, 124, afforded 22 (42). 

Mild oxidation of o-nitrobenzaldehyde arylhydrazones with either bromine and sodium acetate or lead tetraacetate results in the overall loss of two hydrogen atoms and production of a class of iV-aryl heterocycles, tiie structure of which was the subject of uncertainty and some controversy for more than fifty years. These oxidation products were first prepared and investigated by Chattawayj " who described them as isodiazomethanes and formulated them as the triaziridine derivates 72. Structural assignment was based entirely on evidence from degradation studies in particular, Chattaway showed that reduction of... 

A mixture of 30.2 g. (0.20 mole) of o-nitrobenzaldehyde,2 40 g. (0.29 mole) of phenylacetic acid, 100 ml. (1.08 moles) of acetic anhydride, and 20 g. (0.20 mole) of triethylamine is refluxed for 15 minutes in a 500-ml. flask. The solution is cooled to 90°, and 100 ml. of cold water is added over a 5-minute period at a rate that maintains the temperature above 90° (Note 1). The solution is filtered at 95-100° and cooled to 20°. frims-o-Nitro-a-phenylcinnamic acid precipitates in the form of light-orange crystals. It is separated by filtration and washed with 60 ml. of 50% acetic acid and with water. The dried acid weighs 39-42 g. (72-77%) and melts at 195-198°, which corresponds to a purity of about 98% (Note 2). After recrystallization from 500 ml. of toluene, it is in the form of yellow prisms weighing 38-39 g. (71-72%) and melting at 197.8-198.3°. 

A. von Baeyer also synthesized indigo by a fascinatingly simple reaction between o-nitrobenzaldehyde (9) and acetone in alkaline solution. The product, o-nitrophenyllactic acid ketone (10), splits off acetic acid and water and dimerizes to form indigo [12] ... 

The intramolecular hydrogen abstraction has been largely developed for the case of the nitro group [22,37], and is well known for some derivatives of o-nitrotoluene, for o-nitrobenzyl alcohols, ethers and esters [38-40] as well as on the acetals of o-nitrobenzaldehyde [41], With these compounds, the nn (singlet or triplet) state abstracts a hydrogen and the biradical relaxes to the aci-nitro form (the first intermediate is actually observed in bicyclic systems where formation of the nitronic acid is sterically hindered) [41], which under basic conditions dissociates to the corresponding anion [42],... 

Mix the solid test sample with calcium carbonate or, alternatively, evaporate a drop of the test solution to dryness with calcium carbonate both operations may be carried out in the hard glass tube of Fig. 11.58. Cover the open end of the tube with a strip of quantitative filter paper moistened with a freshly prepared solution of o-nitrobenzaldehyde in 2m sodium hydroxide, and hold the paper in position with a small glass cap or a small watch glass. Insert the tube into a hole in an asbestos or uralite sheet and heat the tube gently. Acetone is evolved which colours the paper blue or bluish-green. For minute amounts of acetates, it is best to remove the filter paper after the reaction and treat it with a drop of dilute hydrochloric acid the original yellow colour of the paper is thus bleached and the blue colour of the indigo is more readily apparent. 

Acetate. Mix 20 mg of the substance with 1 ml of ethanol or n-butyl alcohol and 5 drops concentrated H2S04. Heat in the hot water rack for 10 minutes, and pour into 2 ml of Na2C03 solution - characteristic odour of ester (IV.35, 3) OR, better, indigo test (IV.35, 9). Mix 15 mg of the substance with 15 mg of CaC03 in a semimicro test-tube, introduce a pressure-filter tube carrying a strip of filter paper moistened with a solution of 5 mg of o-nitrobenzaldehyde in 1 ml of NaOH solution. Heat the test-tube strongly. Blue or green stain on paper confirms acetate. 

The first anthranil ( azo-opianic acid ) was made by this method in 1881,113 but was not recognized as such. In 1882 Friedlander and Henriques109 prepared the parent compound, by reduction of o-nitrobenzaldehyde with tin and acetic acid. They thought it to be the anhydride of anthranilic acid, and hence arose the name anthranil. It has been shown, using O18, that the carbonyl oxygen is lost, and the cyclic oxygen atom is derived from the nitro group, in the reductive cyclization.141... 

The photochemical rearrangement of o-nitrobenzaldehyde or its acetals to the corresponding o-nitrosobenzoic acid derivatives has been known for many years. A careful study of the mass spectra and metastable ions obtained from methyl o-nitrosobenzoate and o-nitrobenzaldehyde dimethyl-acetal has provided strong evidence that the electron impact induced fragmentation strongly parallels the photochemical rearrangement Eq. (71). 

Other functional groups may be present during reduction. Aromatic amino ethers are prepared by the same general procedures described above, e.g., 772-aminoanisole (80%) and 2-aminodiphenyl ether (94%). The reduction of o-nitrobenzaldehyde to the sensitive o-aminobenzaldehyde is successfully accomplished by the action of ferrous sulfate and ammonia (75%). m-Dimethylaminobenzaldehyde is formed by reduction of the nitro acetal in aqueous solution with sodium sulfide followed by methyla-tion (74% over-all) or by catalytic reduction of m-nitrobenzaldehyde in... 

Concerning bicyclic derivatives, the first 1,2-benzisoxazole, 3-phenyl-l,2-benzisoxazole, was synthesized by treatment of o-nitrobenzophenone oxime with alkali in 1892 <1892CB1498>, and the parent compound was obtained in 1908 <1908ACP47>. In 1881, 5,6-dimethoxy-2,l-benzisoxazole was the first compound of this class to be prepared <1881JPR353>, and in 1882 the unsubstituted system was synthesized by reduction of o-nitrobenzaldehyde with tin in acetic or hydrochloric acid <1882CB2105>. 

Condensation catalyst. Triethylamine serves as basic catalyst for the Perkin condensation of o-nitrobenzaldehyde with phenylacetic acid and acetic anhydride to give a-phenyl-trans-o-nitrocinnamic acid. A student experiment on the condensation of benzaldehyde with the same reactants includes a simple procedure for the separation of the cis- and /rans-isomers. ... 

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