Dimethyl maleate isomerization

In the reduction of dimethyl maleate, isomerization to fumarate was much faster than hydrogenation.171 In addition to a mechanism broadly similar to that for butadiene, a further pathway was thought to operate which involved an ordio-metallation of one PPh3 ligand, as shown in equations... 

In the reduction of dimethyl maleate, isomerization to fumarate was much faster than hydrogena-... 

Independent work by Schmid93 and by Padwa94 on the photochemistry of 2H-azirines has shown that irradiation of such systems leads in the first instance to the formation of nitrile ylids (nitrilium betaines). Subsequent 1,3-addition to a variety of dipolarophiles affords five-membered heterocycles. These additions take place in a stereospecific and regioselective manner thus, irradiation of the diphenyl-2f/-azirine 117 in the presence of dimethyl maleate leads to the formation of the two isomeric 1-pyrrolines... 

Another example of the retention of volatile DA reagents is that of cyclopentadiene in a tandem retro-DA/DA prime reaction [15, 16, 38], This reaction type is the thermal decomposition of a DA adduct (A) and the generation of a diene (generally the initial diene) which is trapped in situ by a dienophile leading to a new adduct (B) [39]. Cyclopentadiene (22) (b.p. 42 °C) is generated by thermolysis of its dimer at approximately 160 °C [40]. An equimolar mixture of commercial crude dicyclopenta-diene (21) and dimethyl maleate was irradiated in accordance with the GS/MW process, in an open reactor, under 60 W incident power, for 4 min (8 x 30 s). The expected adduct 23 was isolated in 40% yield (Scheme 7.1). The isomeric composition of 23 (endo-endoIexo-exo = 65/35) was identical with that obtained under classical conditions from 22 and methyl maleate [41]. The overall yield of this tandem reaction can be increased from pure dimer 21 (61%) and the same tandem reaction has also been reported using ethyl maleate as dienophile [31]. 

Irradiation of the sodium salt 517 in a solution of maleonitrile in THF gave a 30% yield of the as-spiro[2.6]nonatrienedicarbonitrile 524 (Scheme 6.106). Analogously, fumaronitrile led to the trans-diastereomer 525 exclusively in 29% yield [193b], which was also obtained from (trimethylsilyl)tropylium tetrafluoroborate (519) as precursor of 5 [208]. The interception of 5 by dimethyl fumarate succeeded by generating 5 from 517 by either photolysis [193] or thermolysis [193, 194] and from 519 [208] and afforded the dimethyl trans-dicarboxylate 526 in yields of 50, 40 and 42%, respectively. Liberation of 5 in the presence of dimethyl maleate led also to 526 [194, 214], In this reaction, the isomerization of dimethyl maleate to fumarate could have interfered and hence pretended the loss of the stereochemical information, since... 

Photochemical cycloaddition reactions between sydnones (1) and 1,3-dipolarophiles take place to give products which are different from, but isomeric with, the thermal 1,3-dipolar cycloaddition products. These results are directly interpreted in terms of reactions between the 1,3-dipolarophiles and Ae nit mine (316). The photochemical reactions between sydnones and the following 1,3-dipolarophiles have been reported dicyclopentadiene, dimethyl acetylene dicarboxylate, dimethyl maleate, dimethyl fumarate, indene, carbon dioxide, and carbon disulfide. ... 

Kiefer and Okamura 73> demonstrated stereoselectivity with respect to the olefinic component in an allene-olefin cycloaddition. 1,1-Dimethyl-allene with dimethyl fumarate at 160—180 °C gave two cycloadducts, both retaining the trans disposition of ester functions with better than 99% stereoselectivity dimethyl maleate gave the isomeric cis adducts with... 

Cp2V()] -alkene) is synthesized by treatment of vanadocene with aUcene bearing an electron-withdrawing group. The reaction of vanadocene with dimethyl frunarate or dimethyl maleate leads to the formation of the same complex, bis() -cyclopentadienyl)() -dimethyl fumarate)vanadium (72), via isomerization (Scheme 40). 

The dimerization rate constants of dialkyl fumarates [k — 25-120 m s ) [236] decrease with increasing steric hindrance of the alkyl group and prove to be significantly smaller than those of fumaronitrile [k = l x 10 m s ) [240], The elec-trochemically generated dimethyl maleate undergoes rapid cis trans isomerization to the dimethyl fumarate then rapid radical anion dimerization [241], In comparison, the EHD rate constant for 4-methylcoumarin (A = 1.8 x 10 M s ) proved similar to that of a relatively fast cinnamate (4-cyano k — 5.7 x 10 M s ) [242]. 

The details of the electrohydrodimerization of dimethyl maleate in methanol has been studied using Fourier transform infrared (FTIR) spectroscopy [339]. Spectra were recorded as a function of time at a constant applied potential (—1.5 V versus Ag/AgCl) with the reference spectrum being obtained at OV. The result is shown in Fig. 49(a) as plots of dR/R versus the wavenumber (cm" ), where R is the reference spectrum and dR is the sample spectrum minus the reference spectrum. Thus, positive dR/R values indicate loss of chromophore, while negative dR/R values indicate gain of chromophore. The analysis of the spectral data showed that the formation of the hydrodimer, 1,2,3,4-butane tetracarboxylic acid, is accompanied by isomerization of dimethyl maleate (the cis isomer) to dimethyl fumarate (the trans isomer). This is nicely illustrated by Fig. 49(b), from which it is seen that the loss of chromophore at 1390 cm" (cis isomer) proceeds more rapidly than the gain in chronomophore at 1288 cm" (trans isomer). 

Isomerization of the olefinic ligand is observed in the photochemical rearrangement of dimethyl maleate iron tetracarbonyl to dimethyl fumarate iron tetracarbonyl 300.396). 

Iron and copper phthalocyanines catalyze the isomerization of dimethyl maleate to dimethyl fumarate in the vapor phase at 300°C. No catalytic activity was observed in solution (338). Magnesium and zinc phthalocyanines catalyze the polymerization of methyl methacrylate when illuminated (Xm 600 m/i) (197). Manganous phthalocyanine (88) and ferrous phthalocyanine (59) catalyze the aerial oxidation of benzyl alcohol to benzaldehyde. The catalytic oxidation of ascorbic acid, using magnesium and copper derivatives, is light-sensitive (190, 310). a-Tetralin is catalytically oxidized, in the presence of the magnesium, zinc, or iron complexes, to a-tetralone, the reaction being chemiluminescent (60, 61,158,169, 371). The oxidation of luminol to 5-aminophthalazine-l,4-dione, catalyzed by iron phthalocyanine, is also chemiluminescent (61, 345, 361). 

With dialkyl maleates isomerization at the metal takes place before codimerization. Thus a dsjtrans mixture of cycloadducts is obtained e.g. heating of a 1 1 mixture of dimethyl maleate and methylenecyclopropane in the presence of 0.2 mol% (r -C3H,)(Ti -C5H5)Pd/P(/Pr)3 for 8 hours to 100 °C gives a 77% yield of the cycloadduct as a 38 62 cisjtrans mixture. Using the above mentioned pumping technique the yield of the cycloadduct is nearly quantitative after 2 hours at 130 °C with a 90% predominance of the c -isomer... 

SCHEME 4.10 Diels—Alder reactions of isomeric dimethyl maleate and dimethyl fumarate with buta-1,3-diene. 

Bromination-dehydrobromination of ci5,cis,cis-cyclododeca-l,5,9-triene gave a mixture of two products. The minor, isolated in 20% yield, was identified as the symmetrical tribromo-trans-cyclotriene (87), and was treated with base to give cyclododeca-l,5,9-triyne. Neither the major product, nor the products of bromination-dehydrobromination of rrans,rrans,rrans-cyclododeca-l,5,9-triene, could be dehydrobrominated to alkynes. The cyclododeca-l,5,9-triyne was found to be very stable, but reacted with dimethyl maleate at 230°C to give (88) as a mixture of isomers, possibly via prior isomerization to tricyclobutabenzene. ... 

The amine-catalysed isomerization of dimethyl maleate into dimethyl fumarate, proceeding via a conjugate addition-elimination of the amine, has been found to be first order in dimethyl maleate, second order in the amine, and overall third order. DFT calculations at the B3LYP/6-31G(d,p) level revealed a linear correlation between the basicity of the amine and the isomerization rate. ... 

Dimethyl maleate heated 1 hr. with triphenylphosphine at 150° dimethyl fumarate. Y ca. 100%.—Dimethyl citraconate is not isomerized under these conditions. A. R. Hands, Soc. 1964, 1181. 

The cis—trans isomerization of dimethyl maleate to dimethyl fumerate is shown in Scheme 16 and is convention-... 

Dimethyl maleate (9) and dimethyl fumarate (10) are examples of cis and trans isomers, called geometric isomers. Their names do not reflect this isomeric relationship, however, because the parent diacids from which they can be prepared were discovered and named before this stereochemical fact was known. Being diastereomers, these diesters would be expected to have different physical and chemical properties, and indeed they do. The difference in their physical states at room temperature is the most dramatic The maleate 9 is a liquid with a freezing point of about -19 °C, whereas the fumarate 10 is a solid with a melting point of 103-104 °C. 

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