Methoxy adduct

Both syn and anti methoxy adducts were considered (Figure 4). The 6-31+G basis set was employed to give a proper description of the anions by inclusion of diffuse functions. The corresponding AEr and AGr for these... 

The nature of the solvent also determines the chemoselective outcome in the reaction products. Products arising from the incorporation of one solvent molecule are formed (besides dibromides) in alcohols, acetic acid and acetonitrile (Id-e), whereas dibromo derivatives are formed exclusively in chlorinated solvents, nitromethane and in ionic liquids. (9) Chemoselectivity depends on the relative nucleophilicity of the solvent and the counterion, although it is affected also by other phenomena (ion pairing, and ion dissociation) in methanol the addition process gives quasi-exclusively bromo-methoxy adducts, whereas in acetic acid dibromides are the main products, formed in addition to smaller amounts of the bromo-acetoxy derivatives. (70)... 

The same reaction scheme can also explain the stereochemical behavior of the addition of benzeneselenenyl chloride to 108 in methanol, which gives, in addition to the trans adduct 138, the analogous methoxy derivative 146, the cross-bonded chlorides 147 and 148, and the analogous epimeric methoxy adducts 149 and 150 (equation 130). 

The formation of both isomeric chlorides 147 and 148 and the corresponding methoxy adducts 149 and 150 in methanol is at variance with the behavior observed in AcOH/ LiC104, where only the acetoxy species 140 is formed. This has been interpreted by taking into account the possible role of a specifically solvated carbenium ion pair, such as 145, prior to the formation of a free carbenium ion of type 144. 

Murata T, Saito G (2006) Properties of reaction products between cytosine and F4TCNQ in MeOH two hemiprotonated cytosine salts with F4TCNQ radical anion and methoxy adduct anion. Chem Lett 35 1342-1343... 

Barton and co-workers have studied30 the reactions of trifluoromethyl hypofluorite with various alkenes and found that (Z)- and (T -stilbene give vicinal fluoro trifluoromclhoxy products and vicinal difluorides in chlorotrifluoromethane or diethyl ether, while vicinal fluoro methoxy adducts predominate when the reaction is carried out in methanol at —78 C. svn Addition predominates in all cases on the basis of the fluorination regioselectivity of many alkenes, the formation of a /1-fluoro carbcnium ion is proposed.30... 

Fluorine addition with trifluoromethyl hypofluoritc to various uracil and cytosine bases and nucleosides has been extensively studied. Vicinal fluoro trifluoromethoxy or fluoro methoxy adducts, formed mainly by syn addition, are usually hydrolyzed thus resulting in fluoro-sub-stituted derivatives,42 48 e.g. formation of 24 and 25. 

In the case of indene and acenaphthylene slightly syn prevalent fluoro methoxy adduct formation was observed, while in the case of 1-phenyl-substituted benzocyclene triads the profound effect of the structure of the alkene and the reaction conditions on the stereochemical result of the reaction was established.76 ... 

The difference in stability noted above is of the same order of magnitude as that found for the formation of adducts 22 and 23 for the reaction of 1,3,5-trinitrobenzene with the OH" and MeO" ions, respectively. Examination of the activation parameters shows some relevant differences between the heterocyclic and the homocyclic systems, however. The higher reverse rate for the methoxy adduct of trinitrobenzene 23 relative to the corresponding hydroxy adduct 22 is controlled by the higher activation entropy, whereas the higher reverse rate for the methoxy adduct of the dinitropyridine 1 relative to 3 is determined by the activation enthalpy. The entropy effect has been related to the different role of intramolecular interactions of the hydroxy adducts in the benzene and pyridine series. The reason for this difference is still unclear, however.45... 

The methoxy a-adducts 42-44 have been observed by 1H and 13C NMR in the reactions of pyrazinium, quinoxalinium, and pteridinium cations with the methoxide ion (Scheme 39). Measured in methanol-d4 at 20°C, the hydrogen attached to the sp3-carbon atom in the methoxy adducts 42-44 has undergone an upheld chemical shift (between 5.3 and 5.5 ppm) when compared with the chemical shift of the hydrogen on the sp2-carbon atom C-2 in 36, 37, and 40 respectively in the 13C-NMR spectra, the sp3-carbon atom shows an upheld chemical shift between 80.3 and 84.3 ppm (Table II) (86KGS1380). 

H and 13C Chemical Shifts for the Dihydropyrazine Fragment in the H- and l3C-NMR Spectra of the Methoxy Adducts 42-44 ... 

The ability of methoxy adducts 42-44 to add a second molecule of methanol across the C=N bond appears to depend on the C=N carbon electrophilicity. The latter can be estimated by chemical shifts for proton and carbon-13 resonances of the HC=N fragment in the 1H- and 13C-NMR spectra of dihydropyrazines 42-44. 

Preussomerin I 697 and ( )-preussomerin G 698 were obtained from 620 with a five- and six-steps sequence in 15% and 12% overall yield, respectively, through modifications of substituents of the dioxocin ring. Thus, attack of lithium methoxide from the less hindered face of the enone 620, followed by protection of the phenolic oxygen as its methyl ether provided the methoxy adduct 692. The ketone 693 was obtained through a benzylic bromination-solvolysis-oxidation protocol, which required only a single purification. The C(2)-C(3) olefin was introduced by selective silylation of the C-l carbonyl of diketone 693 and oxidation of the silyl enol ether with Pd(OAc)2. Enone... 

The behavior of 2-methoxy-2//-thiopyrans, formed on addition of methoxide anion to 2,4,6-triarylthiopyrylium cations, toward some nucleophiles and electrophiles was investigated (83ZC333 86JPR373). The results are easily accounted for by considering the methoxy-adducts in equilibrium with the parent ions. 

Reactions of /)-benzoquinone and its derivatives with alkoxide ions (RO R = H, Me, Et, i-Pr, PhCH2) in MeCN also result in formation of the corresponding semiquinone radical anions accompanied by the formation of RO-substituted p-benzoquinones, which are the oxidized products of p-benzoquinones [360], Detailed product and kinetic analyses of the reactions indicate that RO-adduct anion of /)-benzoquinone is an actual electron donor and that RO is acting as a very strong base or nucleophile rather than a one-electron reductant in an aprotic solvent, such as MeCN [360], Similarly, the reaction of C o with methoxide anion (MeO ) in benzonitrile (PhCN) results in the disproportionation of Cgo to yield both C(,o and the methoxy adduct [360]. Spectroscopic and kinetic studies also indicate that a methoxy adduct anion of Ceo is a real electron donor and that MeO is acting as a very strong base or nucleophile rather than an electron donor in PhCN [360],... 

Acid-catalyzed procedures typically are either boron trifluoride/methanol (BF3/ CH3OH) or hydrochloric acid/methanol (HCI/CH3OH). Many analysts use sulfuric acid instead of hydrochloric acid. Acid-catalyzed procedures are used for free fatty acids, phospholipids, or triacylglycerols, often at elevated temperatures. Although the procedures are relatively efficient at production of methyl esters, there will be some isomerization of some cis-, trans-isomers to the trans-Ztrans-isomers (136). This isomerization can be reduced by using lower temperatures, for instance 60 °C, for HCI/CH3OH or room temperature for BF3/CH3OH (137). However, under these milder conditions, some phospholipids may not be esterified (137). In addition, methoxy adducts may be formed and hydroxy fatty acids may produce artifacts. 

The reaction of diene adducts with oxidants has also been studied. In both cases cis insertion of the Pd(II)-carbon bond into the second olefinic bond occurred. Thus Stille et al. 126) found that reaction of the norbornadiene(methoxy) adduct or the norticyclyl(methoxy) adduct with CI2 or with Brg in CH3OH gave 3-cx o-methoxy-5-halometricyclenes plus the dimethoxy adduct ... 

Anhydrous potassium phenoxide was prepared by the method of Komblum and Lurie (47). Picryl chloride was prepared from picric acid by published procedures (48). DNBF (16) was prepared by nitration of benzofuroxan (49) and recrystallized from glacial acetic acid. The potassium salt of the methoxy adduct 17 was obtained from the reaction of methanolic DNBF with potassium hydroxide (50). PiDNBT (30) was prepared by cyclization of 2,2, 4,4, 6,6 -hexanitrohydrazobenzene (51) with concentrated sulfuric acid and recrystallized from glacial acetic acid yellow plates mp 291-294 °C (decomposition) NMR [100 MHz, (CH3)2SO-d6] 9.09 (d, 1 HJ = 1.9 Hz), 9.48 (s, 2 H), 9.45 (d, lH,/= 1.9 Hz). 

B.ii.e Carbonylation and Acylation. The keto function in pyrrolo[3,2-c]pyridin-4-ones and pyrido[3,4- ]pyrrolizidin-l-ones can be enolized and triflated to yield the substrates 72 and 73, respectively (Scheme 34). Replacement of the triflyloxy group by carbonylation is effected with palladium catalysis. Reaction of the pyrido[3,4-fc]-pyrrolizidin-l-ones 73 was complicated by formation of a by-product, namely, the 2-methoxy adduct 74. In the latter case competitive palladium-assisted elimination of the triflyloxy group leads to an imminium intermediate, which adds a methoxy group as a... 

That such reactions are competing with other possible modes of reaction is shown by monitoring, by means of n.m.r. spectroscopy, the reaction of 2-chlorotropone with potassium methoxide in dimethyl sulphoxide. In early stages of the reaction the formation of a 7-methoxy-adduct is observed but it rapidly disappears and a... 

The 4-borauracils 129a,b were prepared by condensing a P-boronic amino acid with isocyanic acid or methyl isocyanate followed by Hoffinan elimination (Scheme 45) (2010MI33). The NMR spectrum indicated that the corresponding bis-methoxy adducts form when these compounds are treated with a large excess of methanol. 

There has been no lack of attempts to convert lipids into derivatives which could be chromatographically fractionated and from which the original substances could be subsequently recovered. Acetoxymercuri-methoxy adducts are particularly easily accessible derivatives, being formed by reaction of unsaturated compoimds with a solution of mercuric acetate in methanol containing a little acetic acid. This addition reaction takes place quantitatively at room temperature [68]. ci -Com-pounds react 10—20 times faster than fm i -isomers [68]. The imsaturated compounds can be recovered by treating their adducts with hydrochloric acid, without cis-trans isomerisation or rearrangement of the double bond occurring [68]. 

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