Pyrolysis of lactones

Rearrangements and other side-reactions are rare. The ester pyrolysis is therefore of some synthetic value, and is used instead of the dehydration of the corresponding alcohol. The experimental procedure is simple, and yields are generally high. Numerous alkenes have been prepared by this route for the first time. For the preparation of higher alkenes (> Cio), the pyrolysis of the corresponding alcohol in the presence of acetic anhydride may be the preferable method." The pyrolysis of lactones 9 leads to unsaturated carboxylic acids 10 ... 

Tebbe, Petasis, and alternative alkenylations Pyrolysis of lactones... 

Pyrolysis of lactone tosylhydrazoue salts. Agosta et ai have developed a process that is formally a reversal of the Baeyer-Villigcr oxidation, that is, a method for conversion of lactones into cyclic ketones. An example is the synthesis of the spiro[3.4]-ociane-l-one (5). I he starting material is the lactone (1) this is converted into the... 

In a typical Knof procedure, 3jS-hydroxyandrost-5-en-17-one acetate is epoxidized with perbenzoic acid (or m-chloroperbenzoic acid ) to a mixture of 5a,6a- and 5)5,6)5-epoxides (75) in 99 % yield. Subsequent oxidation with aqueous chromium trioxide in methyl ethyl ketone affords the 5a-hydroxy-6-ketone (76) in 89% yield. Baeyer-Villiger oxidation of the hydroxy ketone (76) with perbenzoic acid (or w-chloroperbenzoic acid ) gives keto acid (77) in 96% yield as a complex with benzoic acid. The benzoic acid can be removed by sublimation or, more conveniently, by treating the complex with benzoyl chloride and pyridine to give the easily isolated )5-lactone (70) in 40% yield. As described in section III-A, pyrolysis of j5-lactone (70) affords A -B-norsteroid (71). Knof used this reaction sequence to prepare 3)5-hydroxy-B-norandrost-5-en-17-one acetate, B-noran-... 

Certain lactones extrude CO2 on heating or on irradiation, such as the pyrolysis of... 

Reaction of commercially available 3-chlorotetronic acid 762, obtained by pyrolysis of methyl 2,4-dichloroacetoacetate at 140 °C in vacuo [235], with o-phenylene-diamine affords, after cyclization-oxidation with AgOAc, the quinoxaline lactone 763 in 69% yield [234] (Scheme 5.83). 

The /3-lactone dimer of dimethylketene can be prepared by pyrolysis of its polyester, which is formed by the base-catalyzed polymerization of dimethylketene.3"6 In addition to the rearrangement of the normal dimer described above,6 the direct dimerization of dimethylketene in the presence of aluminum chloride3 or trialkyl phosphites7 leads to the /3-lactone dimer. 

Numerous procedures for the preparation of butenolides have been developed. Font and coworkers (234-236) prepared the 5-O-substituted derivatives 223a-c of D-ribono-1,4-lactone. The cw-glycol system of223a reacted with ATjV-dimethylformamide dimethyl acetal and then with iodomethane to give the trimethylammonium methylidene intermediate 224. Pyrolysis of 224 gave the butenolide 225. 

The original preparation of y-crotonolactone by Lespieau involved a five-step sequence from epichlorohydrin and sodium cyanide. A recent detailed study of this procedure reported an overall yield of 25% for the lactone. Glattfeld used a shorter route from glycerol chlorohydrin and sodium cyanide hydrolysis and distillation of the intermediate dihydroxy acid yielded y-cro-tonolactone in 23% yield and -hydroxy-y-butyrolactone in 28% yield. The formation of y-crotonolactone in 15% yield has also been reported from pyrolysis of 2,5-diacetoxy-2,5-dihydrofuran at 480-500 . ... 

The endo- and e.vo-Diels - Alder adducts 37a and 38a, which are the products from the reaction of cyclopentadiene and (7 )-angelica lactone 39a, have been alkylated under the usual conditions (LDA, THF, — 78 °C) with iodomethane, ethyl, butyl and benzyl bromide26. The alkylations are all completely diastereoselective as is expected in these tricyclic examples and yields are in the range of 80-95%. Pyrolysis of 37b and 38b at around 250-290°C for 2-6 days led to the butenolides 39b. 

The mechanism of decarboxylation of /3-lactones has attracted much attention. The gas-phase decomposition of 2-oxetanone is a unimolecular first-order process. It has a considerably lower energy of activation than the pyrolysis of oxetane and a much higher entropy of activation, indicating a loose activated complex (69JA7743). The ease of the reaction is greatly affected by the electronic effect of substituents at position-4, but not at position-3. The Hammett treatment of a series of rrans-4-aryl-3-methyl-2-oxetanones gave a good correlation with [Pg.374]

Preparation of tetraalkylallenes by the pyrolysis of 2,2,4,4-tetraalkyl-3-hydroxy-3-butenoic acid /J-lactones at 150°-550°C [129]. 

Certain lactones extrude C02 on heating or on irradiation, examples being pyrolysis of 58,458... 

Fragmentation of 1,3-diols 7-34 Decarbonylation of p-hydroxy carboxylic acids and of p-lactones 7-36 Elimination of CO and C02 from bridged bicydic compounds 7-43 Pyrolysis of P-hydroxy olefins 7-44 Pyrolysis of allylic ethers... 

The volatiles produced by sugar degradation can make an important contribution to flavour. Pyrolysis of glucose at 300 °C allowed 56 compounds to be identified, the main product being l,4 3,6-dianhydroglucopyranose.567 More than 100 volatiles were separated when glucose was heated at 250 °C for 30 min in air or in nitrogen 4-hydroxy-2-pentenoic acid lactone, 1-(2-furyl)propane-l,2-dione, and 3-methyl-cyclopentane-1,2-dione were identified as new products.568... 

Dodecahedradiene 70 has also been prepared and isolated as a stable compound [68, 71]. The highest yields (up to 70%) were obtained by flash vacuum pyrolysis of the bis(lactone) 69, which can easily be prepared along the pagodane route (cf. Scheme 12) [72]. The calculated degree of pyramidalization of the double bonds in 70 (ip = 42.8°) is slightly smaller than that in dodecahedrene 68 (Figure 8). 

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