Aldehydes from aryl nitro compounds

As a preparative method the direct decarboxylation of olefinic acids is almost limited to the formation of styrenes and stilbenes from substituted cinnamic acids. Thermal decomposition of cinnamic acid gives styrene (41%). The yield is nearly quantitative if the reaction is carried out in quinoline at 220° in the presence of a copper catalyst. The yields of substituted styrenes where the aryl radical contains halo, methoxyl, aldehyde, cyano, and nitro groups are in the range of 30-76%. cis-Stilbene and cis-p-nitrostilbene are prepared in this way from the corresponding a-phenylcinnamic acids (65%). One aliphatic compound worthy of mention is 2-ethoxypropene, prepared by heating -ethoxycro-tonic acid at 165° (91% yield). The mechanism of acid-catalyzed decarboxylations of this type has been studied. Isomerization of the double bond from the a,/5- to the /5, y-position before decarboxylation very likely occurs in many instances. ... 

From To - Alkanes Cycloalkanes Alkenes Alkynes Aryls Halogen compounds Alcohols Phenols Ethers, Quinones B. and Si compounds P and 6i compounds Nitro, Nitroso, Azo, Azoxy, Hydrazo, ides Amines Organometallic Aldehydes Ketones Acids, Anhydrides, Esters Arn.des, Amidines, Nitriles Hydroky-aldehydes Amino Heterocycles Nucleosides Miscellaneous, including heterocycles... 

Observations of reactions of the present type with compounds in which the aryl groups are separated by conjugated polyenes date back to 1962.139 There have been several further reports of the process, and Leznoff and co-workers have described the reaction of 1-formylphenyl-4-phenylbuta-l,3-dienes. 140>141 The reaction does not occur with acetyl or nitro-substituents on such compounds since the lowest transition is nrr, but from l-(p-formylphenyl)-4-phenylbuta-l, 3-diene, for example, 1 -(p-formylphenyl)naphthalene and 8-phenyl-2-naphth-aldehyde are formed similar results have been reported for the /w-formylphenyl 134 ... 

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