Dienecarboxylic acid

Etbylenecarboxylic acids from lactones 2,4-Dienecarboxylic acids... 

Equimolar amounts of p-nitrobenzaldehyde, methyl bromoacetate, BU3P, and Zn stirred at 100° for 7 h without solvent E-product. Y 94%. The method is a useful, non-basic, alternative to the Wittig route, and is applicable to aliphatic, aromatic or heterocyclic aldehydes use of 0.5 eq. Zn gave comparable (or better) yields. F.e. incl. 2,4-dienecarboxylic acid esters s. Y. Shen et al.. Tetrahedron Letters 29, 6119-20 (1988). 

Cyano-c[ 5-dienones from pyrylium salts s. 18, 523 ring opening to 5-cyano-2,4-dienecarboxylic acids cf. 30, 203 (1965)... 

The substituted vinyl-)3-lactone undergoes ring-opening isomerization to form 2,4-dienecarboxylic acid in aprotic solvents in the presence of catalytic amount of Pd(OAc)2. Addition of trimethyl phosphite led to almost quantitative isomerization into the unsaturated acid. However, decarboxylation-elimination to form a conjugate diene proceeded in DMF or DMSO.t The quantitative evolution of CO2 in good coordinating aprotic solvents is explained by a poor solvation of the carboxylate anion through the carboxylate (Scheme 12). 

Without additional reagents 2,4-Dienecarboxylic acid amides from cyclopropenones and enamines Insertion of 3-C-atoms into nitrogen-carbon bonds... 

The second pathway involves the formation of 2-hydroxy-cyclopenta-2,4-dienecarboxylic acid methyl ester (P2). This reaction is characterized by a transition state TS4 with an energy barrier of 66.12kcalmol In the transition state structure TS4, the C2=C6 bond loses its double bond character and the O2 molecule binds with the C4 atom and thus a peroxy group is formed. As shown in Figure 19.5, after the formation of transition state structure TS4, the bond between the C4 and C6 atoms is cleaved, and one of the O atoms of O2 binds with the C4 and C6 atoms while the other O atom makes a double bond with the C2 atom. Thus, a neutral product is formed. This product channel is formed exothermically with a reaction enthalpy of-84.68 kcalmol and the reaction is exoergic with a free energy of-82.15kcalmol ... 

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