Saturated Esters

The hydrogenolyaia of cyclopropane rings (C—C bond cleavage) has been described on p, 105. In syntheses of complex molecules reductive cleavage of alcohols, epoxides, and enol ethers of 5-keto esters are the most important examples, and some selectivity rules will be given. Primary alcohols are converted into tosylates much faster than secondary alcohols. The tosylate group is substituted by hydrogen upon treatment with LiAlH (W. Zorbach, 1961). Epoxides are also easily opened by LiAlH. The hydride ion attacks the less hindered carbon atom of the epoxide (H.B. Henhest, 1956). The reduction of sterically hindered enol ethers of 9-keto esters with lithium in ammonia leads to the a,/S-unsaturated ester and subsequently to the saturated ester in reasonable yields (R.M. Coates, 1970). Tributyltin hydride reduces halides to hydrocarbons stereoselectively in a free-radical chain reaction (L.W. Menapace, 1964) and reacts only slowly with C 0 and C—C double bonds (W.T. Brady, 1970 H.G. Kuivila, 1968). 

Esters Saturated esters absorb at 1735 cm esters next to either an aromatic-ring or a double bond absorb at 1715 cm-1. 

Homoenolate Protonation The p-protonation of homoenolates has been observed by Scheidt and co-workers, resulting in a redox transformation of enals to afford saturated esters 48. This process is catalysed by the NHC derived from imidazolium salt 46 and utilises phenol as a proton source [14]. A range of primary and secondary alcohols, and phenol itself, are competent nucleophiles with which to trap the acylazolium intermediate 47 generated by protonation (Scheme 12.8). 

Scheme 12.8 Redox reaction of enals to give saturated esters...

This approach has been applied by Rovis and co-workers to the formation of saturated esters from a-haloaldehydes and alcohols. A range of aliphatic alcohols, phenol and aniline proved competent nucleophiles (Scheme 12.17) [30]. 

Hydrogenation of a,p-unsaturated Raney Ni Saturated esters Fine chemicals. 

Only strong oxidants can react dangerously with saturated esters. Unsaturated esters have often been involved, but the reaction mainly concerns non-saturation the ester group can increase the risk by boosting the double bond reactivity. Therefore, reference to unsaturated esters will be concerned with this type of reaction. 

The only accident that involves a saturated ester is the result of an attempt to extract an organic residue containing hydrogen peroxide with ethyl acetate. The latter was mixed with methanol and refluxed with the residue and hydrogen peroxide in an aqueous solution. A second extraction was carried out with acetate and the liquid was then evaporated. The small quantity of the compound that remained after the evaporation detonated violently. It was thought that this detonation was the result of the violent decomposition of methyl hydroperoxide, peracetic acid and/or ethyl peracetate. 

We have shown that the direct arylation of acrolein toward the synthesis of cinnamaldehyde derivatives was an efficient procedure. Using the palladacycle 1 as catalyst, substituted aldehydes 3 were prepared with up to 87% isolated yield from condensed aiyl bromides (Scheme 21.1, Route 1) that was extended successfully to heteroaiyl bromides, like bromoquinolines (6). Alternatively, the acrolein diethyl acetal was used as olefin and a selective formation of the saturated ester 4 was attained under the same reaction conditions (Scheme 21.1, Route 2). The expected aldehydes 3 were, however, obtained from most of the aiyl halides used under modified conditions. It was shown that the addition of n-Bu4NOAc in the medium... 

As in the case of the oxidation of saturated esters, the rate of chain copolymerization monomer and dioxygen obeys the equation similar to that for aliphatic ester oxidation. 

The trimolecular reaction of dioxygen with double bonds of two molecules of non-saturated esters. As in the case of a similar bimolecular reaction, this reaction seems to be preceded by CTC formation. 

The accumulation of hydroperoxide accelerates the ester oxidation. As in hydrocarbon oxidation, this acceleration is the result of hydroperoxide decomposition into free radicals. The most probable is the bimolecular reaction of hydroperoxide with the weakest C—H bond of saturated ester (see Chapter 4). 

A typical elution profile the separation of saturated esters by gas-liquid chromatography 1. methyl formate 2. methyl acetate 3. ethyl formate 4. ethyl acetate 5. -propyl formate 6. iso-propyl acetate 7. w-butyl formate 8. sec-butyl acetate 9. iso-butyl acetate 10. n-butyl acetate... 

Although the application of tungsten catalyst 5 to the cross-metathesis reaction of other alkenes has not been reported, Basset has demonstrated that to-un-saturated esters [18] and glycosides [21], as well as allyl phosphines [22], are tolerated as self-metathesis substrates. 

Conjugate addition.1 This base undergoes efficient 1,4-addition to a,(i-un-saturated esters to give the enolate of a (3-amino ester, which can be trapped by an alkyl halide to give a-alkyl-(3-amino esters (2) as a mixture of syn- and antiisomers (about 1 1). These esters can be converted into 3-lactams (3) by hydrolysis and dehydration (11, 449) or into a-alkyl-a,3-unsaturated esters (4) by N-quater-nization and 3-elimination on silica gel ( 75% yield). 

Two photochemically induced reactions of substituents have been reported which require the participation of the triazole ring. Irradiation of 3-(l-methyltriazol-4-yl)acraldehyde in methanol gave the saturated ester 23 in high yield, whereas the corresponding quaternary salt 24... 

The reduction of unsaturated esters encompasses the reduction of esters containing double and triple bonds, usually in positions, and/or aromatic rings. Such esters may be converted to less saturated or completely saturated esters, to unsaturated or less unsaturated alcohols or to saturated alcohols. Presence of aromatic rings in conjugation with the multiple bonds facilitates saturation of the bonds. Aromatic rings are hydrogenated only after the saturation of the double bonds. 

Sodium borohydride, even in a very large excess, reduced methyl 2-none-noate and methyl cinnamate incompletely to mixtures of saturated esters, unsaturated alcohols and saturated alcohols [1061]. On the other hand, a,p-unsaturated esters of pyridine and pyrimidine series were converted predominantly and even exclusively to saturated alcohols. Methyl 3-(7-pyri-dyl)acrylate gave, on refluxing for 1-2 hours in methanol with 10 mol of sodium hydride per mol of the ester, 67% of 3-(y-pyridyl)propanol and 6% of 3-(y-pyridyl)-2-propenol methyl 3-(6-pyrimidyl)acrylate gave 77% of pure 3-(6-pyrimidyl)propanol [1061]. 

This result appears reasonable, because the carbonyl activity of saturated esters, i. e. the polymer, usually is higher than... 

We discovered that PCTFE could be added to ethyl acrylate when a stoichiometric amount of chloro(pyridine)cobaloxime(III) was used. In accordance with the IR spectrum of the resulting polymer, the carbonyl band was apparent at 1735 cm-> which corresponded to the C=0 group in a saturated ester. Unfortunately, the decrease in the absorbance of the chloride band at 971 cm-i seemed to be too large, compared with the increase in the absorbance of the carbonyl band, implying that the side reaction also occurred. 

PCTFE was found to add to methyl methacrylate via the use of a stoichiometric amount of chloro(pyridine)cobaloxime(III). In the IR spectrum of the resulting product, the carbonyl group of a saturated ester was shown as a strong band at 1735 cm-1. However, the loss in the chloride band at 975 cm1 was tremendous, and strong, broad bands due to the... 

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