Alkenoic acid

The intramolecular reaction oF allcenes with various O and N functional groups offers useful synthetic methods for heterocycles[13,14,166]. The reaction of unsaturated carboxylic acids affords lactones by either exo- or endo-cyclization depending on the positions of the double bond. The reaction of sodium salts of the 3-alkenoic acid 143 and 4-alkenoic acid 144 with Li2PdCl4 affords mostly five-membcrcd lactones in 30-40% yields[167]. Both 5-hexe-noic acid (145) and 4-hexenoic acid (146) are converted to five- or six-mem-bered lactones depending on the solvents and bases[168]. Conjugated 2,4-pentadienoic acid (147) is cyclized with Li2PdCl4 to give 2-pyrone (148) in water[i69]. 

Hydroxy- and amino carboxylic acids can be dimerized in good to moderate yields, when the substituents are not in the a- or P-position and when they are additionally protected against oxidation by acylation (Table 2, No. 17-19). 2-Alkenoic acids cannot be dimerized but lead to more or less extensive passivation of the anode due to the formation of polymer films [136]. 3- and 4-Alkenoic acids give moderate yields when they are neutraUzed with BU3N or EtjN [136]. 3-Alkenoic acids with the structure... 

Epoxidative lactonization.1 This reaction can be used for a diastereoselective synthesis of 5-hydroxyalkylbutanolides (3) from (E)- and (Z)-4-alkenoic acids (1). Thus epoxidation of (E)-l results in an epoxide (2) that in the presence of acid is converted into erythro-i. In contrast, (Z)-l is converted into threo-3. Yields are essentially quantitative. 

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