Formate esters, pyrolysis

This mechanism of a -elimination reaction is supported by experimental findings with " S- and C-labeled starting materials." The Chugaev reaction is analogous to the ester pyrolysis, but allows for milder reaction conditions—i.e. it occurs at lower temperatures. It is less prone to side reactions, e.g. the formation of rearranged products, and is therefore the preferred method. 

Ester pyrolysis has been shown to be a syn elimination in the case of formation of stilbene by the use of deuterium labels.335... 

Completion of the synthesis of nootkatone simply requires pyrolysis of the formate ester in... 

A number of poly (thiol esters) have been synthesized by method BC (29). The reaction temperature was increased from room temperature to above 200°C. The products were often colored because of side reactions (replacement of hydroxyl with chlorine, formation of ketene structures, and ester pyrolysis are known side reactions in polyester formation). 

The utility of the Chugaev elimination for the formation of olefins without rearrangement of the carbon skeleton can be observed upon pyrolysis of the xanthate of alcohol 14.17 The desired vinyl cyclopropane (IS) was isolated in reasonable yield (42%) along with a small amount of the rearranged xanthate. Alternatively, acid-mediated dehydration with sulphuric acid yielded a variety of rearranged products in low yield. Ester pyrolysis (of the acetate of 14) also furnished a variety of compounds, with the major product being cyclopentene 16. 

A reaction pathway involving a concerted transition state of the type (210) has been shown to be compatible with the kinetic results and formation of 1,2-diarylethanones observed during the gas-phase pyrolysis of the formate ester of benzoin and the... 

The first reaction step is ester pyrolysis under formation of a vinyl ester and a carboxyl end group. 

It was established that the first process implied a statistical rupture of the polyester chains via an ester pyrolysis reaction. The produced gases were identified as H2O, CO2 and 5-hexenoic acid. The second step led to the formation of e-caprolactone (cyclic monomer) as a result of an unzipping depolymerisation process. Figure 12 displays the obtained TG-MS results. 

Ester pyrolysis has been shown to be a syn elimination by use of deuterium labels. In the case of stilbene formation, deuterium was introduced by stereospecific reduction of cis- and trans-stilhene oxide by LiAlD4. The syn elimination is demonstrated by retention of deuterium in the product from the trans epoxide and its elimination in the product from the cis epoxide. 

Pyrolysis at 190° of the resulting diastereomeric A -pyrazolines (8) and (11) leads to elimination of nitrogen and formation of the cis- and tmns-cydo-propanecarboxylates (9) and (12), respectively. Thermal decomposition of the A -pyrazoline (13) affords methyl tiglate (14) in addition to the cyclopropane derivative (15) in a ratio 2 1, while A -pyrazolines such as (3) give only 0L,[i- or, y-unsaturated esters, and no cyclopropane derivatives. 

In the case of the cyclohexane derivative 7 however, that bears an equatorial acetate group, two axial cis-/3-hydrogens are available, and elimination in both directions is possible. The pyrolysis of 7 yields the two elimination products 8 and 6. Formation of product 8 is strongly favored, because the new double bond is in conjugation to the ester carbonyl group. ... 

Scheme 6.8 gives some examples of ketene-alkene cycloadditions. In Entry 1, dimethylketene was generated by pyrolysis of the dimer, 2,2,4,4-tetramethylcyclobutane-l,3-dione and passed into a solution of the alkene maintained at 70° C. Entries 2 and 3 involve generation of chloromethylketene by dehydrohalo-genation of a-chloropropanoyl chloride. Entry 4 involves formation of dichloroketene. Entry 5 is an intramolecular addition, with the ketene being generated from a 2-pyridyl ester. Entries 6, 7, and 8 are other examples of intramolecular ketene additions. 

The color of the polymer can also be affected by inappropriate reaction conditions in the polymerization process, such as temperature, residence time, deposits of degraded polymer or the presence of oxygen. Degradation of polyesters and the generation of chromophores are thermally effected [29b, 29c, 39], The mechanism of thermal decomposition is based on the pyrolysis of esters and the formation of unsaturated compounds, which can then polymerize into colored products. It can be assumed that the discoloration takes place via polymerization of the vinyl ester end groups or by further reaction of AA to polyene aldehydes. 

One of the routes to epimestix>l begins with acylation of estradiol with benzoyl chloride to give the dibenzoate 5. Pyrolysis of the ester leads to formation of the 16,17-olefin. Hydroxylation by means of osmiiim tetroxide affords the cis-diol 7 due to the intermediacy of the cyclic osmate ester (6a)-, attack... 

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