Maleate esters

Free-radical reaction rates of maleic anhydride and its derivatives depend on polar and steric factors. Substituents added to maleic anhydride that decrease planarity of the transition state decrease the reaction rate. The reactivity decreases in the order maleic anhydride > fumarate ester > maleate ester. 

Two-step 1,4 cycloaddition of enamines, such as was observed with methyl vinyl ketone, is not possible with acrylate or maleate esters. This is due to the fact that, following the initial simple substitution, no side-chain carbanion is available for nueleophilic attack on the a carbon of the iminium ion. Likewise two-step 1,3 eycloaddition, such as that found when alicyclic enamines were treated with acrolein, is impossible with acrylate or maleate esters because transfer of the amine moiety from the original enamine to the side chain to form a new enamine just prior to the final cyclization step is not possible. That is, the reaction between a seeondary amine and an ester does not produce an enamine. 

A special sulfonation technique is also used for the production of sulfosuccinates (Fig. 1.16). These are derived from maleate esters or half esters using a suitable sulfonation agent, most commonly sodium metabisulfite. 

EM is assumed to be 109 M for all phthalate esters, and 3 x 109 M for all maleate esters m Eberson, 1964. The reaction is eighty times faster than that of methyl phthalate under these conditions (using activation energy = 23 kcal mol-1)... 

The applicability of axially chiral 1, l -binaphthalcnc-8,8 -diol in asymmetric Diels-Al-der reactions was studied by Fuji and colleagues190. They studied the Lewis acid catalyzed reaction of the unsymmetrically substituted maleate ester of 1,1 -binaphthalene-8,8 diol 302 with cyclopentadiene. The diastereoselectivity proved to depend strongly on the Lewis... 

There have been a number of isolated studies of metal-ion catalyzed nucleophilic reactions of other groupings. Particularly interesting is the induced nucleophilic attack on olefins. Hydration is normally very sluggish. Enzymes can speed up such reactions. Aconitase, an iron-containing enzyme, catalyzes the isomerization of citric acid to isocitric acid, through the intermediacy of cis-aconitic acid. A possible mechanism has been suggested based on the following Co(III) model chemistry. Rapid cyclization of the maleate ester produces Ai and AS chelated malate half ester ... 

Aue and Thomas62 have described the addition of DMAD to a variety of imino ethers. The azetines 1 and 2 reacted readily in dichloro-methane to give a 50 50 mixture of fumarate 4 and maleate esters 5 in greater than 50% yield. 

A consequence of the addition of coordinated OH- to alkenes is that other nucleophilies, for example a coordinated aminate ion, should also be active. This type of reaction is seen with the chloropentaammine complex [Co(NH3)500CCH=CHC02Bu,]2+ in aqueous base533 (Scheme 49). The reaction of the f-butyl maleate complex occurs to the extent of ca. 50% and is complicated by hydrolysis of the maleate ester and some decomposition of the cobalt(III) complexes. Reactions of this type have recently been exploited in the synthesis of j3-carboxyaspartic acid in the coordination sphere of cobalt(III).53... 

This method has been applied to the rigid 3-bond dyad, DNM[3]M, (Fig. 37), in which the maleate ester group (M) serves as the acceptor (the DCV acceptor group cannot be used because the energies of the singlet and triplet +DMN[3]DCV CS states all lie above the 3[ DMN[3]DCV] locally excited triplet state, see Fig. 29). Benzophenone (BP) was used as the sensitiser, and a highly polar solvent... 

Selectivity in cycloadditions to maleates is mentioned first. The stereoselective cycloadducts produced in maleate cycloadditions are all 2,3-cis-pyrrolidines, indicating that the aryl or 1-alkenyl substituents as R are overlapping with one of the maleate esters in the transition state. More azomethine ylides show high stereoselectivity to dimethyl maleate than to dimethyl fumarate. Thus, there are several azomethine ylide 1,3-dipoles in Table IX that show high stereoselectivity to maleate but poor to fumarate. The N-unsubstituted azomethine ylides RCH=NH —CH COOR, derived from the imines of a-amino esters, are highly endo selective to maleimides, but poor in stereoselectivity to dimethyl maleate on the contrary, the N-substituted derivatives RCH=NR —CH COOR are nonstereoselective to maleimides, but exclusively stereoselective to the maleate. 

Heck (91) reported that acetylenes can be carbonylated to give substituted maleate esters. Propiolate esters are formed as side products. The reaction scheme is as follows ... 

A bicyclic monomer containing a maleate ester unit (M-43) undergoes a very slow 2,6-addition polymerization with 1-12 (X = Cl)/CuCl/L-l in the bulk at 130 °C to afford narrow MWDs (Mw/Mn 1.2) (11% conversion in 2 weeks).223 Enchainment of this monomer to the chlorine-terminated polystyrene increases the decomposition temperature of the polymer. 

Moad also notes that the most common grafting modifications made to polyolefins are via maleic anhydride, maleate esters, styrene, maleimides, acrylates and their esters, and vinyl silanes. Other polymer systems (Fink, 2005) that undergo grafting are polystyrene/maleic anhydride (useful for PA6/PS blends), PVC/butylmethacrylate (for improved processi-bility), PET/nadic anhydride, starch/vinyl acetate and starch/methyl acrylate (for improved water resistance). 

---