Aldehydes aromatic rings

In general, imines are too reactive to be used to protect carbonyl groups. In a synthesis of juncusol, however, a bromo- and an iodocyclobexylbnine of two identical aromatic aldehydes were coupled by an Ullmann coupling reaction modified by Ziegler. The imines were cleaved by acidic hydrolysis (aq. oxalic acid, THE, 20°, 1 h, 95% yield). Imines of aromatic aldehydes have also been prepared to protect the aldehyde during ring metalation with. -BuLi. ... 

When the additional nitrogen atom is included in one of the aromatic rings, on the other hand, there is obtained a compound with antihistaminic properties. Reaction of the Grignard reagent from 4-chlorobromobenzene with pyridine-2-aldehyde gives the benzhydrol analog (12). The alcohol is then converted to its sodium salt by means of sodium, and this salt is alkylated with W-C2-chloroethyl)dimethylamine. Carbinoxamine (13) is thus obtained. ... 

Mehrling and Welde first determined if hydro-aromatic ring aldehydes in general gave violet like odours when condensed with acetone, and it was found that in the case of the four following aldehydes only the first yields a body having a violet odour —... 

Aldehydes Saturated aldehydes absorb at 1730 cm-1 aldehydes next to either a double bond or an aromatic ring absorb at 1705 cm-1. 

One further comparison aromatic aldehydes, such as benzaldehyde, are less reactive in nucleophilic addition reactions than aliphatic aldehydes because the electron-donating resonance effect of the aromatic ring makes the carbonyl group less electrophilic. Comparing electrostatic potential maps of formaldehyde and benzaldehyde, for example, shows that the carbonyl carbon atom is less positive (less blue) in the aromatic aldehyde. 

Notable examples of general synthetic procedures in Volume 47 include the synthesis of aromatic aldehydes (from dichloro-methyl methyl ether), aliphatic aldehydes (from alkyl halides and trimethylamine oxide and by oxidation of alcohols using dimethyl sulfoxide, dicyclohexylcarbodiimide, and pyridinum trifluoro-acetate the latter method is particularly useful since the conditions are so mild), carbethoxycycloalkanones (from sodium hydride, diethyl carbonate, and the cycloalkanone), m-dialkylbenzenes (from the />-isomer by isomerization with hydrogen fluoride and boron trifluoride), and the deamination of amines (by conversion to the nitrosoamide and thermolysis to the ester). Other general methods are represented by the synthesis of 1 J-difluoroolefins (from sodium chlorodifluoroacetate, triphenyl phosphine, and an aldehyde or ketone), the nitration of aromatic rings (with ni-tronium tetrafluoroborate), the reductive methylation of aromatic nitro compounds (with formaldehyde and hydrogen), the synthesis of dialkyl ketones (from carboxylic acids and iron powder), and the preparation of 1-substituted cyclopropanols (from the condensation of a 1,3-dichloro-2-propanol derivative and ethyl-... 

From a study of the decompositions of several rhodium(II) carboxylates, Kitchen and Bear [1111] conclude that in alkanoates (e.g. acetates) the a-carbon—H bond is weakest and that, on reaction, this proton is transferred to an oxygen atom of another carboxylate group. Reduction of the metal ion is followed by decomposition of the a-lactone to CO and an aldehyde which, in turn, can further reduce metal ions and also protonate two carboxyl groups. Thus reaction yields the metal and an acid as products. In aromatic carboxylates (e.g. benzoates), the bond between the carboxyl group and the aromatic ring is the weakest. The phenyl radical formed on rupture of this linkage is capable of proton abstraction from water so that no acid product is given and the solid product is an oxide. 

At elevated temperatures, methylene carbons cleave from aromatic rings to form radicals (Fig. 7.44). Further fragmentation decomposes xylenol to cresols and methane (Fig. 7.44a). Alternatively, auto-oxidation occurs (Fig. 1.44b ). Aldehydes and ketones are intermediates before decarboxylation or decarbonylation takes place to generate cresols and carbon dioxide. These oxidative reactions are possible even in inert atmospheres due to the presence of hydroxyl radicals and water.5... 

The condensation of aromatic rings with aldehydes or ketones is called hydroxy-alkylation. The reaction can be used to prepare alcohols, though more often the alcohol initially produced reacts with another molecule of aromatic compound (11-12) to give diarylation. For this the reaction is quite useful, an example being the preparation of l,l,l-trichloro-2, 2-bis (p-Chlorophenyl) ethane (DDT) ... 

Methyl groups on an aromatic ring can be oxidized to the aldehyde stage by several oxidizing agents. The reaction is a special case of 19-14. When the reagent is... 

The aldehyde acid reactions have already been described generally in Chapter 2. There it was pointed out that a nucleophilic attack at a carbonyl group is particularly easy when this is attached to an aromatic ring that bears an electron withdrawing group at position 4. The reactivity of the carbonyl group is greatly increased in acid medium ... 

Use of benzotriazole in the preparation of diphenylmethanes and triphenylmethanes has been reviewed." Benzotriazole is condensed with an aldehyde and then allowed to react with naphthols to form a diphenyl-methane benzotriazole derivative such as 69 (Scheme 9). The benzotriazole moiety in 69 is displaced by a Grignard reagent to give triphenylmethanes.79 100 This method allows for the preparation of triarylmethanes which contain three different aromatic rings. Compounds 70-72 are prepared by this method. 

All the 7,8-secoberbines incorporate an JV-methyltetrahydroisoquinoline moiety with two or three oxygenated substituents at C-l, C-2, and C-3. The lower aromatic ring possesses four substituents in a vicinal arrangement of which two are alkoxyls and the third the berbine bridge carbon. The latter may occur in different oxidation states as an aldehyde (in 1 and 2), an alcohol (3-6, 8, 9), or a carboxylic acid (7). 

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