Lactones conjugated dienes

The reaction of alkenyl mercurials with alkenes forms 7r-allylpalladium intermediates by the rearrangement of Pd via the elimination of H—Pd—Cl and its reverse readdition. Further transformations such as trapping with nucleophiles or elimination form conjugated dienes[379]. The 7r-allylpalladium intermediate 418 formed from 3-butenoic acid reacts intramolecularly with carboxylic acid to yield the 7-vinyl-7-laCtone 4I9[380], The /i,7-titisaturated amide 421 is obtained by the reaction of 4-vinyl-2-azetidinone (420) with an organomercur-ial. Similarly homoallylic alcohols are obtained from vinylic oxetanes[381]. 

COi is another molecule which reacts with conjugated dienes[10,95,96], COt undergoes cyclization with butadiene to give the five- and six-membered lactones 101. 102. and 103, accompanied by the carboxylic esters 104 and 105[97.98], Alkylphosphines such as tricyclohcxyl- and triisopropylphosphine are recommended as ligands. MeCN is a good solvent[99],... 

The above bicyclization could be extended to functionalized diynes, permitting the preparation of lactams or lactones having a fused exocyclic conjugated diene, a representative example of which is shown in Eq. 9.53 [98],... 

Likewise, a-methylene-/3-lactones, 280, can serve as allene equivalents since they cycloadd to conjugated dienes to provide the expected [2 + 4] products, e.g. 281 and 282, which on heating fragment with carbon dioxide loss to furnish the allene adduct 279 again [116]. 

A recently described method for insertion of a carbon monoxide molecule into the monoepoxide of a conjugated diene gives /3-lactones in high yield. This is achieved by reaction of iron pentacarbonyl with the starting vinyloxirane to give the 7r-allyl iron complex (66), which on oxidation with cerium(IV) ammonium nitrate gives the /3-lactone. In some cases, y-Iactone products can also be obtained from this reaction (8lJCS(Pi)270). 

In accord with their unusually high reactivity, cyclopropanones may undergo various types of cycloaddition reactions. In addition to Diels-Alder type addition with conjugated dienes (4+3- 7 cycloadditions), substituted cyclopropanones also react with aldehydes forming dioxo-lanes (3 +2->-5), and with ketenes yielding (3-lactones (2 +2- 4).118>... 

In addition to the polymerization of conjugated dienes Nd-alcoholates are mainly used for the polymerization of cyclic polar monomers like lactones, lactides, e.g. see [247] and carbonates, e.g. see [248]. 

Let us bear in mind that for compounds of the 3-ionone series we can consider two possibilities of reaction through six-center transition states leading respectively to heterocyclic rings (lactone or oxide) and to isomers with exocyclic conjugated diene structures. The two mechanistic t3rpes are shown in Figure 1. 

Cyclization afforded a combined 77% isolated yield of the lactone 137 and the y-hydroxy ester 138 the hydroxy ester could be converted to the lactone in a straightforward manner, thus allowing it to be used to throughput additional material to the target structure. Unfortunately, these materials were accompanied by the formation of the conjugated diene 136, a substance that undoubtedly arises via the intervention of acid-base chemistry, leading to -elimination of the silyloxy unit from 135. 

The overall procedure of the spiro y-lactone and 7-lactone synthesis can be considered as a molecular-assembling process in which three simple independent species (i.e., a conjugated diene, a ketone, and carbon dioxide) are used to build a complex organic molecule in a well-controlled fashion. 

Table 4 Synthesis of Spiro y-Lactones from Conjugated Dienes, Ketones, and COj...

The first enantioselective formal total synthesis of paeonilactone A was reported by J.E. Backvall who used a palladium(ll)-catalyzed 1,4-oxylactonization of a conjugated diene as the key step. The lactonization precursor diene acid was obtained from an enantiopure dimethyl malonate derivative via sequential Krapcho decarboxylation and ester hydrolysis. 

Conjugated dienes, enones, ene-esters, ene-lactones, and diene-esters as exciton... 

Keywords Living polymerization, Living copolymerization, Rare earth metal complexes, Alkyl methacrylate, Alkyl acrylates, Lactones, Ethylene, 1-Olefins, Conjugated dienes, Acetylene... 

Allylic bromination by NBS can be applied with success not only to olefins but also to <%,/ -unsaturated ketones, carboxylic esters, nitriles, and lactones. Radical-formers must be added when NBS is used for allylic bromination of conjugated dienes, for side-chain bromination of aromatic or heterocyclic compounds (see p. 198), or for replacement of tertiary hydrogen atoms next to a C=C bond. 

Fig.(9) The transformation of the Wieland-Miescher ketone (1) to the conjugated diene (93) is described. It was converted to the diketone (95) whicch proved a potencial intermediate for the epoxy dilactone (98). The cleavage of the lactone ring of (98) yielded alcohol which was converted a-methylene-Y-butyrolactone (101) by a series of organic reactions. The opening of the epoxide ring of (101) gave the product (102) whose methacrylate derivative on deformylaton provided eriolanin (104).

Corey et al. reported the reaction of singlet oxygen with conjugated diene 203, which was obtained from the isomerization reaction of a,(3-unsaturated lactone 202 using a catalytic amount of DBN. The resulting peroxide intermediate 204 was converted to ( )-folskolin (205) [60] (Scheme 7.47). 

I The saponins isolated in the plant possess aglycones of three skeletons cycloartane, ursane and oleanane, with some variation in each structure—type. It s very interesting to discover such cycloartane-type saponins, that its side-chain has been modified naturally to conjugated diene-carboxylic acid, which formed amide with 2 -amino-3, 4 -dimethyl-y-lactone moiety. 

Conjugated dienes undergo hydroperfluoroalkylation with perfluoroalkyl iodides and zinc in the presence of titanium catalysts 02 Yields are moderate to good (52-74%) but stereoselectivity is low. From allylic halides functionalized on the a-vinylic position (TMS, carboxylate, phosphonate), additions to terminal alkynes provide functional dienes, used in further synthetic reactions leading to lactones and carboxylic or phosphonic esters.228... 

In the 1,4-diacyloxylation, two carboxylate anions are added in a 1,4 manner to a conjugated diene in an oxidative process involving the removal of two electrons. The catalyst employed is a palladium(II) salt, usually Pd(OAc)2- The 1,4-diacyloxylation may be an intermolecular or an intramolecular process. In the latter case the result is a lactonization. In most cases the stereochemistry of the 1,4-addition of the two carboxylates to the 1,3-diene can be controlled to give either a 1,4-cis or l,4-tra s adduct. 

The prediction of product structure is difficult for such cycloadditions. The difficulty arises from the fact that either the ketene carbonyl group or olefinic linkage can act as the two-electron component. Indeed, in such cycloadditions, both modes of addition can be observed. When 3,3,4,4,5,5-hexamethyl-l,2-bis(methylene)cyclopentane 9 and diphenylke-tene were reacted in cyclohexane at 55 °C for long period of time, virtually equal amounts (70%) of dihydropyran 10 and the cyclohexenone 11 were obtained (Scheme 5). Compound 10 can be readily isomerized in acidic media to afford the conjugated diene 12. When the reaction of 1 with 9 was performed in benzonitrile instead of cyclohexane, the ratio of 10 11 rose from 1 1 to 3 1 (1987JCS(CC)1804). Interestingly, when the reaction was carried out in the presence of a Lewis acid such as ZnCla, two equivalents of diphenylketene was consumed which reacted with the diene to furnish a bicyclic lactone. 

Pd(0)-catalyzed reaction of bromoacrylic acid 15 with various conjugated dienes afforded lactones in moderate to good yields. Annulation to 1,3-cycohexadiene afforded lactones 17 (Scheme 5). After oxidative addition of 15 to Pd(0), a vinylpalla-dation should produce the intermediate 7r-allylpalladium complex 16, which via cii-migration of coordinated carboxylate would produce the cii-lactone 17. 

The substituted vinyl-)3-lactone undergoes ring-opening isomerization to form 2,4-dienecarboxylic acid in aprotic solvents in the presence of catalytic amount of Pd(OAc)2. Addition of trimethyl phosphite led to almost quantitative isomerization into the unsaturated acid. However, decarboxylation-elimination to form a conjugate diene proceeded in DMF or DMSO.t The quantitative evolution of CO2 in good coordinating aprotic solvents is explained by a poor solvation of the carboxylate anion through the carboxylate (Scheme 12). 

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