Efficient synthesis of maleopimaric acid N-arylimides

Abstract

An efficient approach toward synthesis of maleopimaric acid N-arylimides starting from rosin maleic anhydride adduct without isolation of maleopimaric acid has been elaborated. Terpenoid diimide diacids and their esters have been synthesized based on the obtained N-arylimides. Thermal stability of the products has been estimated by derivatography.One of the promising applications of renewable wood-chemical raw materials is synthesis of certain valuable chemicals. The best accessible individual terpenoid compound isolated from adduct of rosin (product of pine turpentine treatment) with maleic anhydride is maleopimaric acid I, a convenient synthon for preparation of compounds possessing a wide range of useful properties and application. Aliphatic amides, imides, and amide-imides have been the described among nitrogen-containing derivatives of maleopimaric acid [1-4]; the compounds have shown a set of valuable properties such as hepatoprotective [2], nematicidal [3], fungicidal, and bactericidal [4] activities. Only a few representatives of acid I aromatic imides have been known; for example, 4-aminophenyl imide [5] converted into thermally stable poly(amido)imides [6], N-(2-methyl-α-naphthyl)imide displaying antineoplastic activity [7], and 4-carboxyphenyl imide prepared from levopimaric acid and pcarboxyphenylmaleic acid imide [8]. At the same time, aromatic imides as well as aliphatic imides may possess diverse biological activity. Since maleopimaric acid is an accessible chiral acid, it may be used for separation of optical isomers of amines [9] provided that the labile anhydride group is converted into the fragment inert towards amines. Maleopimaric acid Narylimides serve as suitable substrates.Maleopimaric acid 4-phenyl-(4-methyl-, 4-hydroxy-, 4-bromo-, 4-amino-, 3-amino-, and 3-carboxyphenyl)imides have been prepared earlier [10] via refluxing of a mixture of individual acid I with the corresponding amine (taken in 10 mol % excess or in equimolar amount) in toluene or pyridine. Reaction of 3-and 4-aminophenylimides with substituted benzaldehydes of vanillin series afforded biologically active azomethines [11,12].This work aimed to elaborate an efficient method of synthesis of maleopimaric acid N-arylimides IIIa-IIIl from accessible adduct of rosin with maleic anhydride and aromatic amines IIa-IIl without isolation of individual acid I (refluxing in toluene during 40 h). The rosin-maleic anhydride adduct with content of maleopimaric acid I of about 57% was prepared via treatment of rosin with maleic anhydride [13,14].Under the elaborated conditions, maleopimaric acid I as a component of the adduct reacted with aromatic amines IIa-IIl via the anhydride group to form exclusively N-arylimides IIIa-IIIl as insoluble precipitates that could be easily separated off the unreacted tar acids, well soluble in toluene. Such preparation of N-arylimides avoided the stage of maleopimaric acid isolation, allowing to significantly reduce the process duration and amount of the consumed organic solvents; the target imides could...