Acetates elimination with

The isolation of acyl and carboalkoxy complexes proves that the insertion of CO into both a Pd-alkyl and into a Pd - OR species occurs easily. Quite interestingly, it has been found that CO inserts only into the Pd - OCH3 bond of the complex [Pd(CH3)(OCH3)(P - P)] and that after insertion methyl acetate eliminates with the formation of [Pd(CO)2(P - P)] [131]. 

Vinyl acetate reacts with the alkenyl triflate 65 at the /3-carbon to give the 1-acetoxy-1,3-diene 66[68]. However, the reaction of vinyl acetate with 5-iodo-pyrimidine affords 5-vinylpyrimidine with elimination of the acetoxy group[69]. Also stilbene (67) was obtained by the reaction of an excess of vinyl acetate with iodobenzene when interlamellar montmorillonite ethylsilyl-diphenylphosphine (L) palladium chloride was used as an active catalyst[70]. Commonly used PdCl2(Ph3P)2 does not give stilbene. 

Zn is determined by direct titration with EDTA with xelenol indicator after iron elimination with acetate ions and copper - with sulfide ions. 

Many carbamates have been used as protective groups. They are arranged in this chapter in order of increasing complexity of stmcture. The most useful compounds do not necessarily have the simplest stmctures, but are /-butyl (BOC), readily cleaved by acidic hydrolysis benzyl (Cbz or Z), cleaved by catalytic hy-drogenolysis 2,4-dichlorobenzyl, stable to the acid-catalyzed hydrolysis of benzyl and /-butyl carbamates 2-(biphenylyl)isopropyl, cleaved more easily than /-butyl carbamate by dilute acetic acid 9-fluorenylmethyl, cleaved by /3-elimination with base isonicotinyl, cleaved by reduction with zinc in acetic acid 1-adamantyl, readily cleaved by trifluoroacetic acid and ally], readily cleaved by Pd-catalyzed isomerisation. 

Treatment of the substrate (34) with catalytic (Ph3P)4Pd and dppe provided the desired bicyclo[3.3.0]octanes (35) and the acetate elimination product (36). The choice of ligand is crucial in this case since using only dppe or Ph3P increased the amount of (36). On the other hand addition of BSA (N,0-bis(trimethylsilyl) acetamide) minimized this side product (Scheme 2.12) [24]. 

A second reason for the larger isotope effect observed by Jones and Maness (140) might be that in the less polar acetic acid solvent, there might be a small degree of E2 elimination (with solvent acting as base) superimposed on the dominant Sn 1 mechanism. Such an elimination would involve a primary kinetic deuterium isotope effect with a kn/ko s 2 to 6, and hence even a 1 to 5% contribution from such a pathway would have a significant effect on the experimentally observed kinetic isotope effect. 

Enol (9) comes from available dkione (10) and the synthesis was performed on the enol acetate (11) rather than enol (9). Elimination with strong base gave (6) and the synthesis was completed by Wolf-Kishner removal of the carbonyl group. 

For liquid/liquid partitioning, sodium chloride and a mixture of cyclohexane and ethyl acetate are added to the homogenate. The mixture is again intensively mixed and allowed to stand until the phases separate. An aliquot of the organic phase is dried with sodium sulfate and concentrated. The concentrated residue is mixed with ethyl acetate and the same volume of cyclohexane. Remaining water is eliminated with a mixture of sodium sulfate and sodium chloride, and the solution is filtered. The extract is subjected to cleanup by GPC (Module GPC). 

Transformations of Methyl 5-0-Benzyl-2-0-methyl-/3-I)-glueofuranosidurono-6,3-lae-tone (86) to Dimethyl (Z,E)-2-Methoxy-5-(phenylmethoxy)-2,4-hexadienedioatevl (87). ( Elimination employing DBU b oxidation with silver oxide-sodium hydroxide followed by diazomethane esterification c acidic glycoside cleavage, oxidation by dimethyl sulfoxide-acetic anhydride with formation of 5-0-benzyl-2-0-methyI-D-glucaro-1,4 6,3-dilactone, elimination by using DBU, followed by short treatment with diazomethane d elimination by DBU with subsequent diazomethane esterification e sodium borohydride in hexamethylphosphoric triamide 1 catalytic oxidation followed by short treatment with diazomethane " dimethyl sulfoxide-sulfur trioxide-pyridine-triethylamine.150)... 

Another approach is based on the palladium-catalyzed intramolecular carbocyclization of the allylic acetate moiety with the alkene moiety (Scheme 96). After the formation of a 7t-allylpalladium complex, with the first double bond the intramolecular carbometallation of the second double bond occurs to form a new C-C bond. The fate of the resulting alkylpalladium complex 393 depends on the possiblity of /3-elimination. If /3-elimination is possible, it generates a metallated hydride and furnishes the cycloadduct 394. This cyclization could be viewed as a pallada-ene reaction, in which palladium replaces the hydrogen atom of the allylic moiety.231... 

Two convenient methods have been developed for the preparation of trifluoro-methyl-substituted alkoxyallenes. Reductive elimination of allylic acetates 30 with samarium diiodide leads to 31 (Scheme 8.11) [38], whereas reaction of Wittig cumu-lene 32 with phenyl trifluoromethyl ketone (33) and thermolysis of the intermediate 34 provides 35 (Scheme 8.12) [39]. 

Although there are other unsaturated compounds that will undergo addition-elimination with free radicals, the benzyl ketene acetal XIV appears to be the most active double bond as far as rate of addition is concerned and the most efficient as far as regards to the extent of elimination is concerned. A comparison with the list of chain transfer agents listed in the Polymer Handbook (23) indicated that only the sulfur compounds appear to be more effective than XIV. Hydrolysis of the end-capped oligomer gives a macromer that is terminated with a carboxylic acid group. 

This report describes a process to produce vinyl acetate with high selectivity from exclusively methanol, carbon monoxide, and hydrogen. The simplest scheme for this process involves esterifying acetic acid with methanol, converting the methyl acetate with syn gas directly to ethylidene diacetate and acetic acid, and finally, thermal elimination of acetic acid. Produced acetic acid is recycled. Each step proceeds in high conversion and selectivity. 

Another work of Duhamel and Ancel [59] related this synthesis of retinal via (3-ionylideneacetaldehyde. Condensation of methallyl-magnesium chloride with diethyl phenyl orthoformate (EtC CHOPh) led after bromination of the ene-acetal, deshydrohalogenation (NaOH 50%), ethanol elimination with hexamethyldisilazane (HMDS) and ISiMes, to the bromo-dienol ether. This latter was submitted to bromine lithium exchange and the lithio enol ether was then condensed with p ionylideneacetaldehyde to give retinal, Fig. (28). 

An interesting application of acetal elimination from sugars that is promoted by base is the formation of furanoid and pyranoid glycals from isopropylidene acetals of ftiranosyl and pyranosyl halides.285-287 Treatment of 2,3 5,6-di-0-isopropylidene-a-D-mannofuranosyl bromide (289) with a base gave the fiiranoid glycal 290. The yield was... 

Pharmacokinetic data with radiolabeled melengestrol acetate showed that the parent compound and/or its metabolites are primarily eliminated with the feces (16). At 6 h postdosing, total radioactivity in heifer liver, fat, kidney, and muscle tissues was 9-15 ppb, 7-8 ppb, 1.2-1.8 ppb, and 0.5-1 ppb of melengestrol acetate equivalents, respectively. In fat, most of this radioactivity (80%) was found to be due to the parent drug, while in liver, kidney, and muscle tissues the parent drug represented about 37%, 30%, and 45% of the total residues, respectively. 

Another route that has been recommended recently is oxidation of the As-stenyl acetate to the corresponding 7-kctone, conversion to the p-tosylhydrazone, and elimination with lithium hydride. Overall yields are in the range 20-50%.2... 

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