Preferential elimination

Preferential elimination of hydrogen fluonde from vicinal halofluoro compounds occurs also in the cyclohexane series [55 56, 57], acenaphthene series [55], and benzodihydrofuran series [59 60] Here, the strength of the base and the stereochemistry play important roles... 

Another convenient method for the preparation of tertiary enamines involves the dehydrogenation of saturated bases with mercuric acetate (111-116). A trans-1,2 elimination occurs, which requires an antiperi-planar position of the nitrogen-free electron pair and the eliminated atom. A preferential elimination of the hydrogen atom from the tertiary carbon atom is supposed. Overoxidation can be avoided by adding disodium ethyl-enediaminotetraacetate to the reaction mixture (117). 

The next step of the Peterson olefination allows for the control of the E Z-ratio of the alkene to be formed by proper choice of the reaction conditions. Treatment of /3-hydroxysilanes 5 with a base such as sodium hydride or potassium hydride leads to preferential -elimination to give alkene 3a as major... 

As usual, tertiary substrates do not give the reaction at all but undergo preferential elimination. However, tertiary (but not primary or secondary) halides R3CCI can be converted to primary amines R3CNH2 by treatment with NCI3 and AlCl3 in a reaction related to 10-53. 

The hemidecarboxylation of sodium phthaiate on reaction with mercuric acetate in boiling water [Eq. (82), X = H] (90) was the first reported thermal decarboxylation. The reaction has been observed for a number of arenes with two adjacent carboxylate groups (1-4,91) and has been named the Pesci reaction (91). Studies of 3-substituted sodium phthalates or of preformed mercuric 3-substituted phthalates have shown that the sterically hindered carboxyl group (the 2-carboxyl) is preferentially eliminated whether X is electron-donating or electron-withdrawing [Eq. (82), X = Me (91), Cl, N02 (91,93), Br (93), or C02H (94)]. A similar conclusion was drawn from the decomposition of mercuric 1,2-naph-thalenedicarboxylate and 3,4-phenanthrenedicarboxylate (91). 

To simplify the synthetic effort required to deposit such films, attempts were made to deposit films by pyrolyzing tetrafluoro-p-xylene (F4C8H6). Under similar reaction conditions, a polymer film was deposited that was different from poly(tetrafluoro-p-xylylene) as the FTIR spectrum indicates that it contains more hydrogen and less fluorine. Presumably HF is preferentially eliminated rather than H2. 

On treatment with sodium ethoxide in ethanol, methyl 2,4,6-tri-O-methyl-a- (72) and -/3-D-ribo-hexosid-3-ulose yielded l-deoxy-2-methoxy-4,6-di-0-methyl-D-hex-l-en-3-ulose (73) and several isomeric ethyl 2,3,6-tri-0-methylhexosid-3-uloses (74) (see Scheme 10).133 On alkaline degradation of methyl 2,3-di-0-ethyl-6-0-pro-pyl-a-D-xy/o-hexosid-4-ulose (75) with sodium 1-butoxide in 1-butanol, one mole of ethanol was released per mole of 75, indicating that the substituent at C-2 was preferentially eliminated. On mild, acid hydrolysis of the product, methanol, ethanol, and some 1-propanol were formed, consistent with fission at C-l, C-3, and, to some extent, C-6 (see Scheme 10).134... 

Methyl radical loss from [3-methylbenzofuran]t gives a minor peak at m/e 77. In contrast, expulsion of a methyl radical from the [M-CO]t ion derived from 7-methoxy-4-methyl-coumarin is facile. Deuterium labelling experiments confirmed that the methoxy methyl group is preferentially eliminated (66JCS(C)1712). 

Halogens attached to pyran or pyranone rings have a reactivity comparable with that of alkyl halides but there is some difference in reactivity for example the 2-halogen of 2,3-dichlorotetrahydropyran (712) is the more reactive (76CR(C)(282)357) and is preferentially eliminated in the reaction of 5,6-dibromo-5,6-dihydropyran-2-one (713) with a base... 

The tertiary amine bridge of 9 is preferentially eliminated by peroxy acid oxidation to give 1,2,3,4-tetrafluoronaphthalenc (10) 22° no epoxidation of the C = C bond in the starting compound is observed. Almost the same yields are achieved when using 30% hydrogen peroxide in refluxing methanol.220... 

Dehydrohalogenation of 1 //-2-chlorodecafluorocyclohexane (38B) gives products 39 and 21.79 Preferential elimination of hydrogen fluoride occurs in compound 38B, where hydrogen and fluorine are in an antiperiplanar conformation. 

Preferential elimination of hydrogen fluonde occurs also in highly fluorinated lH -chlorodecafluorocyclohexanes and m 1H,1,2-dichlorononafluorocyclahex-anes [57] It takes place predominantly but not exclusively only m those isomers where hydrogen and fluorine are m antipenplanar conformation When hydrogen and fluorine are in synplanar positions, only hydrogen chlonde is eliminated on treatment with 18 N potassium hydroxide at room temperature for 14 h [57] (equation 28)... 

M. R. Daha. 1991. Kupffer cell depletion in vivo results in preferential elimination of IgG aggregates and immune complexes via specific Fc receptors on rat liver endothelial cells. Clin. Exp. Immunol. 86 328-333. 

FEP has a considerably lower thermal stability than PTFE and starts to degrade at temperatures above 200°C (392°F). There are essentially two stages in the degradation of FEP. The first involves preferential elimination of HFP from the backbone in the second the remaining backbone undergoes decomposition at the same rate as that of PTFE.7... 

Naturally the implication arose that there should be a high incidence of common peptides in the partial hydrolyzates of each of the serum proteins. This, of course, is the same implication that arose in Block s mind (3). Since 1956 this laboratory has been busy trying to isolate common peptides from each of the serum proteins as obtained from electrophoresis on starch slabs. In order to be able to prepare each of the protein hydrolyzates simultaneously we examined nonenzy-matic procedures and devised the dilute acid partial hydrolyzate method which has recently been described in detail (33, 34). In this method aspartic acid is preferentially eliminated from the peptide chain, the re-... 

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