Aldehydes from aryl acetic acids

He made both starting materials from esters of the corresponding aryl acetic acids 53 and 56 by reduction and substitution (in the case of the phosphonium salt). This gave added flexibility as either component can be used as the phosphonium salt 55 or the aldehyde 54. He used the unusual reducing agent REDAL [NaAlH2(0CH2CH20Me)2] instead of DIB AL to make the aldehyde 54. 

Condensation of 2-hydrazinobenzoxazoles (286) with aromatic aldehydes in glacial acetic acid yields 3-aryl[l,2,4]triazolo[3,4-Z>]benzoxazoles (288) <88BCJ1339). Similarly, 3-aryl-9/7-[ 1,2,4]tri-azolo[4,3-Z>]benzimidazoles (287) are obtained from 2-hydrazinobenzimidazoles (289) (Equation (80)) <88BCJ1339>. 

The second category of aldehyde dehydrogenases are efficient catalysts of the oxidation of both aryl and alkyl aldehydes to the corresponding carboxylic acids. The most well known and common of such reactions is the oxidation of acetaldehyde, derived from alcohol, to acetic acid. 

Cinnamic acid synthesis from aryl aldehyde and acetic anhydride. 

Aryl -a-aminopropionic acids are obtained by reduction of azlactones with phosphorus and 50% aqueous hydriodic acid in glacial acetic acid. Many other reducing agents have been used. Reviews of this synthesis and related reactions have been made. The azlactones are conveniently prepared in good yields from aromatic aldehydes and N-acyl derivatives of glycine. Potassium carbonate has been found to be a superior catalyst for this condensation. Ketones cannot be substituted for the aromatic aldehydes. ... 

For example, oxidation of acenaphthene by red lead in acetic acid gives 7-acenaphthenol acetate, from which 7-acenaphthenol is obtained by saponification with methanolic sodium hydroxide. Phenols may be prepared indirectly from aromatic aldehydes by oxidation with peracetic acid followed by hydrolysis of the resulting aryl formate. "... 

With mixed diaryl or alkyl aryl anhydrides, the regioselectivity of attack by the tetracarbonylferrate is, not surprisingly, too poor to be synthetically useful. However, the reagent can be usefully applied to the mixed carboxylic alkylcarbonic anhydrides (23), giving aldehydes after treatment of the intermediate acylferrates with acetic acid (equation 3). The substrates (23) are readily available from carboxylic acids by treatment with ethylchloroformate and triethylamine. Unfortunately the quoted g.c. yields are variable e.g. benzaldehyde, 41% p-tolualdehyde, 76% nonanal, 51%), suggesting that further development may be required. 

Routes via o-aminophenylpyrroles present the most convenient syntheses of a wide variety of pyrrolo[l,2-a]quinoxalines. Thus reaction of the amino compound 6 with acetic anhydride in acetic acid gave the acetamido derivative which was cyclized with phosphoryl chloride to give the 4-methyl compound 7 (R = Me) in 56% yield. The 4-phenyl compound 7 (R = Ph) has been prepared similarly. An even more convenient synthesis of 4-aryl compounds is achieved by reaction of compound 6 with aromatic aldehydes to give the 4,5-dihydro derivatives These are readily oxidized to 4-arylpyrrolo[l,2-a]quinoxalines 9 with manganese dioxide. This approach may be carried out in one step by reaction of compound 6 with aromatic aldehydes (e.g., benzaldehyde) in the presence of cupric acetate. Reaction of the aminophenylpyrrole 6 with 90% formic acid gave pyrrolo[l,2-a]quinoxaline (7, R = H) directly in 98% yield. Pyrrolo[l,2-a]quinoxalines substituted in the l-position and the 7-position have also been prepared from appropriately substituted... 

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