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Dimethyl fumarate, formation

In the [2 + 2] cycloadditions of 10 with iV-phenylmaleimide and dimethyl fumarate, the major cycloadducts were formed with a very high degree of ee transfer from 1,3-dimethylallene8. Similar results were obtained in the reaction of 10 with 1,1-dichloro-2,2-difluoroethene. The reaction with less reactive 1,1-diphenylethene did not lead to cycloadduct formation, but resulted in racemization of the chiral 1,3-dimethylallene instead9, which implies reversible formation of the diradical intermediate in this case. Finally, the cycloaddition of 1,3-dimethylallene to methyl propiolate (14) afforded two cycloadducts, 15 and 16, to which >40% of the initial ee had been transferred (equation 5)11. [Pg.332]

If the solution of methyl diazoacetate is dropped through the condenser the diazo compound is further diluted by the refluxing solvent. This simple technique diminishes formation of dimethyl fumarate and dimethyl maleate as side products. [Pg.193]

The formation of [2+2] cycloadducts has been observed to occur upon irradiation of t-1 with a number of electron-poor alkenes. The reaction of It with dimethyl fumarate has been investigated in the greatest detail. Irradiation of dilute solutions of t-1 and dimethyl fumarate in nonpolar solvent results in the formation of t-1 and dimethyl y-truxinate, 34 (76). At high... [Pg.188]

The reaction of t-1 with dimethyl fumarate is proposed to occur via the weakly fluorescent singlet exciplex intermediate (76). Increasing the solvent polarity results in a decrease in both the exciplex fluorescence intensity and the cycloaddition quantum yield, presumably due to radical-ion pair formation. The low efficiency of cycloaddition from c and the absence of triplet cycloaddition indicate that a planar stilbene chromophore is necessary for exciplex formation (see also Sections V-B and C). [Pg.189]

At high concentrations of t-1, irradiation with dimethyl fumarate yields 34 and a mixture of isomeric oxetanes, 37 (76). Based on the concentration dependence of truxinate and oxetane formation, it was proposed that oxetane formation occurs upon reaction of the t-1 excimer with dimethylfumarate (eq. 18). [Pg.189]

In the presence of trifluoroacetic acid, irradiation of dimethyl acetylenedi-carboxylate and benzene leads to the formation of dimethyl fumarate and dimethyl maleate in appreciable amounts in the absence of acid, only traces of these compounds were detected [36,61], Irradiation of dimethyl acetylenedicarboxylate and benzene in the presence of tetracyanoethylene (TCNE) produces a 1 1 1 adduct at the expense of cyclooctatetraene. The photoaddition still proceeds readily behind a fdter transmitting at wavelengths >290 nm, where only the acetylene absorbs to a significant degree [60],... [Pg.14]

In nonpolar solvents, the cyclobutane 44 is the only product upon irradiation of trans-stilbene/dimethyl fumarate mixtures. Exciplex emission, the detection of a weak ground state complex, as well as the stereospedfity of the cyclobutane formation support the proposed mechanism outlined in Eq. (26). [Pg.249]

Ibata was the first to show that the masked carbonyl ylide embedded within the isomiinchnone framework would readily undergo 1,3-dipolar cycloaddition with various dipolarophiles [34], The isolable isomiinchnone 4 was observed to react with dimethyl fumarate to produce cycloadduct 7 which possesses the 7-oxa-2-azabicyclo[2.2.1]heptane skeleton. When the reaction of 1 was carried out using catalytic amounts of Cu(acac)2 in the presence of various dipolarophiles, smooth dipolar cycloaddition was observed to occur giving mixtures of endo and exo isomers. In most cases, the exo isomers were favored. All of Ibata s isomiinchnone cycloadditions contain aromatic substituent groups, presumably selected to facilitate dipole formation. The synthetic utility of the cycloaddition reaction is diminished, however, because of the low reactivity of the aromatic substituents toward further manipulation. [Pg.123]

Dihydrophosphetes are also available by the action of the electron-rich metallophosphaalkene 45 with electron-deficient alkenes such as dimethyl fumarate, fumarodinitrile, and methyl acrylate, as shown in Eq. (12).24 Ring formation is most likely initiated by a stepwise [2+2] cycloaddition and completed by rapid dimethylamine elimination from transient phosphetane 46. The ferriophosphaalkene 45 is smoothly converted into 2-methylene... [Pg.14]

Similarly small rate factors were obtained for 1,3-dipolar cycloadditions between diphenyl diazomethane and dimethyl fumarate [131], 2,4,6-trimethylbenzenecarbonitrile oxide and tetracyanoethene or acrylonitrile [811], phenyl azide and enamines [133], diazomethane and aromatic anils [134], azomethine imines and dimethyl acetylenedi-carboxylate [134a], diazo dimethyl malonate and diethylaminopropyne [544] or N-(l-cyclohexenyl)pyrrolidine [545], and A-methyl-C-phenylnitrone and thioketones [812]. Huisgen has written comprehensive reviews on solvent polarity and rates of 1,3-dipolar cycloaddition reactions [541, 542]. The observed small solvent effects can be easily explained by the fact that the concerted, but non-synchronous, bond formation in the activated complex may lead to the destruction or creation of partial charges, connected... [Pg.191]

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). [Pg.5049]

In other cases the one-electron transfer mediated mechanism for rearrangement and final adduct formation is only a conjecture, a possibility, an alternative interpretation. Might it be involved in the reaction of (135) with dimethyl methylenemalonate leading to (136) ° or of dimethyl fumarate with (137) to give (138) 272... [Pg.78]

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). [Pg.162]

When 5 is treated with dimethyl fumarate or with frani-l,2-dibenzoylethene, tetramethylcyclopropene is liberated with formation of the ligand exchange product. ... [Pg.2861]


See other pages where Dimethyl fumarate, formation is mentioned: [Pg.198]    [Pg.51]    [Pg.57]    [Pg.94]    [Pg.18]    [Pg.161]    [Pg.352]    [Pg.161]    [Pg.112]    [Pg.32]    [Pg.152]    [Pg.276]    [Pg.112]    [Pg.189]    [Pg.190]    [Pg.323]    [Pg.18]    [Pg.1447]    [Pg.129]    [Pg.27]    [Pg.323]    [Pg.437]    [Pg.139]    [Pg.56]    [Pg.138]    [Pg.32]    [Pg.48]    [Pg.53]    [Pg.54]    [Pg.72]    [Pg.293]    [Pg.1032]    [Pg.578]    [Pg.51]    [Pg.57]    [Pg.848]   
See also in sourсe #XX -- [ Pg.402 ]




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