Methyl 2,4-pentadienoates

Structurally rather complicated target molecules can be synthesized with the aid of thi-olate 1,6-addition reactions to acceptor-substituted dienes as well. For example, a richly functionalized proline derivative with a 2,4-pentadienal side chain was converted into the corresponding 6-phenylthio-3-hexen-2-one derivative by 1,6-addition of phenylthiolate, treatment of the adduct with methyl lithium and oxidation (equation 46)127. The product was transformed into acromelic acid A, the toxic principle of clitocybe acromelalga ichimura. Similarly, the 1,6-addition reaction of cesium triphenylmethylthiolate to methyl 2,4-pentadienoate served for the construction of the disulfide bridge of the macrobicyclic antitumor depsipeptide FR-901,228128. 

We have observed with the above catalyst system that both butadiene conversion and methyl 2, 4-pentadienoate selectivity increase when the catalyst is recycled. Over a series of seven recycle experiments, conversion increases from the low 20 s to 32.2 mole % and selectivity increases from the low 70 s to 83.2 mole % (See Table III.). Conversion and selectivity reach steady state after the third catalyst recycle. 

Stereochemistry is largely lost in die diene vinylation, at least at 100 C, as evidenced by die reaction of (Z,E)-3-methyl-2,4-pentadienoic acid shown in equation (40). 

Fig. 9.5 The prototypical Diels-Alder reaction is that between 1,3-butadiene and ethene, to form cyclohexene. The Diels-Alder reaction has been used in the synthesis of complex natural products above, methyl 2,4-pentadienoate reacts with 1,4-benzoquinone to form an intermediate in the synthesis of the drug reserpine. In a one-pot reaction two carbon-carbon bonds are made and three chiral centers ( ) are created with the correct relative orientations (i.e. essentially one diastereomer is formed)...

Conjugated dienes are a special substrate for the TMM synthon because they can potentially undergo [3 + 2] as well as [4 + 3] cycloaddition. While dimethyl ( . )-muconate gives only seven-membered ring [4 + 3] adducts, methyl 2,4-pentadienoate reacts exclusively at the terminal double bond with (79) to give a vinylmethylenecyclopropane (equation 100). The diphenyl system (81) also reacts with simple 1,3-dienes to produce only diphenylidenecyclopentanes in the presence of Ni or Pd catalysts (equation 101). ... 

Simple, neutral electron-rich imines are generally not useful dienophiles unless q>propriately reactive dienes are used. Thus it is possible to effect cycloadditions of neutral imines with some electron-deficient dienes. - In a series of p rs, Langlois and coworkers have described Diels-Alder reactions of cyclic imines and methyl 2,4-pentadienoate to afford adducts used in alkaloid synthesis. For example, the cycloadditicMi shown in equation (IS) was used in a total synthesis of the indole alkaloid vincamine (45). 

Other 1,3-dienes, such as 1,3-butadiene, isoprene and methyl-2,4-pentadienoate, either do not react with methylenecyclopropanes or yield only 3-vinylmethylene-cyclopentane derivatives exclusively (Table 10 and Eq. 114). Quite unexpectedly, methyl-2,4-pentadienoate reacts only at the terminal C=C bond, giving a vinyl-methylenecyclopentane in poor yield 224) (Eq. 114). 

In a very similar manner, tandem 1,6- and 1,4-additions of -dicarbonyl compounds to methyl 2,4-pentadienoate were utilized by Danishefsky and coworkers- foi the formation of several bi- and tricyclic ring systems. For example, reaction of the enolate of dimedone with this ester gave the expected 1,6-addition product protonation/deprotonation set the stage for a subsequent intramolecular 1,4-addition (equation 9). Likewise, a ketodiester was used to transform the pentadienoate in a one-pot procedure by consecutive 1,6- and 1,4-additions into a richly functionalized tricyclic product which was then converted into the natural product ( )-cpiclovane (equation 10). According to this principle, Irie and coworkers obtained several decalin-2,7-diones by treatment of 2-methylen-2-cyclohexenones with dimethyl 3-oxoglutarate. 

Addition of hydrogen is selective for the double bond further from the electron-withdrawing group thus, the major alkene formed on selective reduction of ethyl 4-methyl-2,4-pentadienoate is the a,/3-unsaluralcd ester (equation 1). The reaction proceeds under mild conditions and in the presence of oxygen. 

Enamines undergo [4 + 2]cycloaddition with electrophilic alkenes such as ethyl sorbate, methyl 2,4-pentadienoate , penta-2,4-dienol , hexa-3,5-dien-2-... 

Abscisic add [abscisin II, ABA histor. name dormin (2Z,4 )-5-((5)-l-hydroxy-2,6,6-trimethyl-4-oxo-2-cyclohexenyl)-3-methyl-2,4-pentadienoic acid]. 

While the intermolecular reactions of butadiene and related methyl or simple alkyl-substituted dienes have been investigated extensively, relatively few examples of the Pd-catalyzed linear dimerization of higher dienes have been reported. Brun and co-work-ers in an isolated paper reported that, under palladium catalysis, reaction of methyl 2,4-pentadienoate (Scheme 9, 28) affords the linear dimer 29 in high yield (95%). Two aspects of this reaction are of particular interest, (i) The dimerization yields essentially only the tail-to-tail dimer 29, not the head-to-tail or head-to-head isomers (30 or 31, respectively). This is in contrast to the behavior of alkyl-substituted dienes under similar conditions vide infra), (ii) Although no details are given, the authors imply that 29 is... 

Ketone [162585-05-9]. 5- l-Hydroxy-2,2-dimethy 1-6-methylene-3-oxocyclohexy[)-3-methyl-2,4-pentadienoic acid, r-Hydroxy-3 -oxo-y-ionylideneacetic acid... 

Hydroxy-2,2-diinethyl-6-methyIenecyclohexyl)-3-methyl-2,4-pentadienoic acid, 9Ci... 

Dihydroxy-2,2-dimethyl-6-methylenecyclohexyl)-3-methyl-2,4-pentadienoic acid Me ester, in D-30155 1,6-Dihydroxy-3,11(13)-eudesmadien-12-oic acid Me ester, in D-30171 3-Hydroxy-6-methoxy-7( 11 )-eremophilen-12,8-olide, in D-30168... 

---