Dimethyl maleate hydrogenation

Dimethyl succinate [106-65-0] (mp 19°C, bp 196°C at atmospheric pressure) can be produced from methanol and the anhydride or the acid, or by hydrogenation of dimethyl maleate (38,39). The same methods can be used to prepare diethyl succinate [123-25-1] (mp — 18°C, bp 216.5°C at atmospheric pressure) and diisopropyl succinate [924-88-9]. 

More recent processes involving the oxidation of butane to a maleic anhydride intermediate, using both fixed-bed and fluidized-bed processes, have been commercialized. The maleic anhydride is subsequently hydrolyzed to maleic acid or esterified in the presence of methanol to dimethyl maleate, which can be reduced to BDO in the presence of hydrogen and catalyst. These processes are attractive due to the low cost of the butane feedstock. The method of choice to make BDO is often dictated by the local availability of the desired chemical feedstock. 

Photochemical hydrogen abstraction reaction for the silylimine 161 give an o-quinodimethane intermediate 162 which could be trapped with dimethyl fumarate, dimethyl maleate, trans-methyl cinnamate, methyl acrylate, acrylonitrile (equation 94)... 

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... 

I he cycloaddition reactions generally give exo adducts with 1 -unsubstituted pyrroles, but 1 -methyl and 1 -trimethylsilyl substituents favor the endo stereoisomers. Cycloaddition has been achieved with. V-phenylmaleimide, methyl acrylate, methyl crotonate, dimethyl maleate, acrylonitrile and crotonitrile. The rate of cycloaddition is increased by 2,5-dimethyl substitution and this is attributed to the affect on the equilibrium between the 2,3 and 3,4-complexes. The isolation of azanorbornenes from the adducts by oxidative demetallation frequently leads to cycloreversion but azanorbornanes can be isolated by hydrogenation immediately after oxidation. <95JA3405>... 

The benzo derivative (128) reacts as a thiocarbonyl ylide. Addition of N-(p-tolyl)maleimide gives a mixture of the exo (71%) and endo (16%) adducts (129 Ar=p-tolyl), which in hot acetic acid eliminate hydrogen sulfide giving the pyrido[l,2-a]benzimidazole (130 Ar=p-tolyl). Analogous 1 1 cycloadducts (131) are formed with dimethyl maleate, dimethyl fumarate, methyl crotonate and methyl acrylate. In contrast to the transformation (129) —> (130), treatment of the adducts (131 R = H, Me) with hot acetic acid gives the tetracyclic compounds (133) via the benzimidazole derivatives (132 R = H, Me). Reaction with alkynic 1,3-dipolarophiles gives pyrido[l,2-a]benzimidazole (134) by desulfurization of the primary adducts (80CL1369). 

By contrast, 1,2,4-triazole carbene 354 displays electrophilic character. Thus, it reacts with alcohols and amines producing triazoline derivatives 355 in quantitative yields. Oxygen or sulfur gives triazolinone and triazolinethione derivatives 356 (similar reaction with tellurium is known for imidazol-2-ylidenes). Reactions of 354 with dimethyl maleate or dimethyl fumarate lead to compounds 357, probably via ring opening of a cyclopropane intermediate with subsequent 1,2-hydrogen shift. 

Compound 87 (R = r-Bu, R = Ph, R = H) has been prepared by addition of tert-butylmagnesium chloride to 1-phenylphthalide (102) and subsequent dehydration with p-toluenesulfonic acid. It is described as a yellow oil with brilliant fluorescence under UV light, which on oxidation with sodium dichromate yields diketone 103. Compound 87 (R = /-Bu, R = Ph, R = H) with dimethyl acetylenedicarboxylategives 104(mp 128-129 C, 80%) on reduction 105 is obtained 105 is also accessible from 87 (R = <-Bu, R = Ph, R = H) and dimethyl maleate (mp 151-152°C, endo) a maleic anhydride adduct has also been described (mp 147.5-148°C, 83%). Diels-Alder adducts have been also prepared from the benzo[c]furan precursors 106 (R = CHjPh, R = H, Ph) in the presence of catalytic amounts of acid 107 (mp 141-142.5X, 70%) and 108 (mp 140-141.5°C, 49%) were obtained, which on catalytic hydrogenation (Pd/C) gave the exo isomers 109(110-1 irC) and 110(90-92°C, 125.5-127°C, dimorphism). The basis for these stereochemical assignments remains unclear, however. Compounds... 

The trans addition of BrF by A -bromoacetamide and hydrogen fluoride to dimethyl maleate and fumarate leads to dimethyl (2X, 3S )-2-bromo-3-fluorosuccinate [(25, 36 )-ll] and (25. 3/ )-2-bromo-3-fluorosuccinale, [(2S. 3/f )-ll], respectively. 

With [RhCbfPyla], DMF and NaBH4, diphenylacetylene is hydrogenated to frans-stilbene as the sole product, while dimethyl acetylenedicarboxylate is converted to dimethyl maleate, and butyne-l,4-diol to c j-but-2-ene-1,4-diol. ... 

The easy access to acyl radicals by photocatalyzed selective abstraction of the carbonyl hydrogen atom in aldehydes has originated further convenient applications. For example, trapping of these nucleophilic radicals by electrophilic olefins gave rise to unsymmetrical ketones. A low amount (2mol.%) of tetrabutylammonium decatungstate (TBADT) as the photocatalyst was sufficient. Scheme 2.8 shows as an example the synthesis of p-ketoester 16 in 63% yield upon photolysis of an acetonitrile solution of heptaldehyde and dimethyl maleate." ... 

The ferrocenyl P,N-ligands 143A and 143B differ in ability to form hydrogen bonds in the transition state of 1,3-dipolar cyloaddition involving azomethine ylides and dimethyl maleate, and they give rise to adducts of opposite enantiomeric series. ... 

The use of hydrogen acceptors enables reaction of unstable molecules at lower temperatures. Examples of hydrogen acceptors are sulfur or selenium [4], a-ole-fins [5], dimethyl maleate [6], diethyl maleate or fumarate [7], and chloranil [8]. Table 1 lists some reactions which employ hydrogen acceptors. 

The dehydrogenation to aromatic compounds becomes more complex when groups such as hydroxy, carbonyl, and acid anhydride are attached to the ring (Table 1, Schemes 3-5) [6,29-35]. The reaction is then usually performed under milder conditions in the liquid phase by the use of a solvent. Common solvents are high boiling-point aliphatic ethers or esters and the typical catalyst is Pd on activated charcoal. When the conditions are optimized conversion and selectivity can be very high (> 95 %). Reaction 5 is an example of the use of a hydrogen-acceptor molecule (dimethyl maleate). The conditions for reaction 4(b) deseiwe a closer look. The reaction is performed in the gas phase with a low surface-area... 

Pyrex-filtered irradiation in de-aerated acetonitrile solution. The resultant enols can be trapped by dimethyl maleate to yield the adducts (27) and (28) in the ratios and yields shown. Trapping of the enols can also be acomplished using dimethyl acetylenedicarboxylate or ethyl propiolate as the dienophile. A study of the phototautomerism of methyl salicylate (29) into (30) at 77 K has been carried out and this again involves a 1,5-hydrogen transfer. Interestingly, the authors report that triplet state emission occurs from the transient keto form (30). The influence of aryl substituents (p-Me and -MeO) upon the photochemically induced intramolecular proton transfer in salicylic acid has also been studied in detail. 

---