Pulvinone

The application of 2-aryl O- methyltetronic acids (388) and (390) in the total synthesis of pulvinone pigments found in Aspergillus tereeus and Suillus grevillei has been reported. 

Regioselective reductions of the maleic anhydride derivatives (387) and (389) with lithium aluminum hydride yielded (388) and (390). Metallation of the O-methyltetronic acid (388) with lithium N- cyclohexyl-A- isopropylamide followed by treatment with, for example, p-anisaldehyde led to pulvinones such as (391) (79JCS(P1)70). 

A highly diastereoselective method for the synthesis of tetronic acids has heen developed based upon a tandem Claisen condensation/transesterification between arylacetate enolates and arylmethylene-substituted 2,2-dimethyl-l,3-dioxolan-4-ones. The versatility of this method has been demonstrated in an improved synthesis of (Z)-configured pulvinones (Equation 58) <20078118>. 

Diketones (35) were needed to synthesise tetronic acids (34) and hence the natural products pulvinones. FGI on (35) gives -hydroxy ketones (36). These cannot be made by a benzoin condensation (Chapter 23) as the aldehyde required would enolise. The acyloin reaction in the presence of Me SiCI avoids this difficulty. 

Olefination reactions of the phosphonates (254) and (255) derived from hydantoin and 1-methylhydantoin, respectively, provide good yields of the expected C-5 unsaturated hydantoin derivatives (256), generally as mixtures of isomers. 52 Heterocyclic analogues, e.g. (257), of pulvinones and, e.g. (258), of permethylated pulvinic acids have been synthesized by Wadsworth-Emmons reactions of the phosphonates (259) and (260), themselves prepared directly from substituted maleic anhydrides. 55 The reaction of ylide (261) with aldehydes to give (262) has been used as a key... 

Patenden et al. [46] synthesized heterocyclic analogues of pulvinones 52-55 and of permethylated pulvinic acids 56, 57 which were found in higher fungi (Scheme 21). All compounds possessing lactonic structures were synthesized in the Horner-Wittig reaction using the corresponding heteroaryl aldehydes and 4-dimethoxy-phosphorylated lactone 58. The latter was obtained as the main product in the reaction between substituted maleic anhydrides 59 and sodium dimethyl phosphite via the postulated carbene. 

Earlier, Knight and Pattenden 419, 421) had synthesised the per-methyl derivative (121) of the pigment (115) from the metallated te-tronic acid (120) and 3,4-dimethoxybenzaldehyde as shown in Scheme 18. Subsequently, the anti-inflammatory properties of several pulvinone derivatives have been recognised and a further synthesis of ( )- and (Z)-pulvinones has been developed 153),... 

Scheme 19. Hypothetical biosynthetic pathway to the pulvinone nucleus...

Alternatively, the pulvinone nucleus of pigment (115) could derive via oxidative decarboxylation of the hypothetical intermediate (9) already implicated in the biosynthesis of grevillins, terphenylquinones (and hence pulvinic acids), and the pigment (10). 

Several hydroxylated diarylcyclopentenones closely related to the pulvinic acids and pulvinones are found in some species of Boletales (Table 13). Their presence indicates the close relationship of Gyrodon to Gyroporus and the Paxillaceae and is strong evidence for inclusion of the gastroid Chamonixia in Boletales. 

Knight, D.W., and G. Pattenden Synthesis of Pulvinones, Metabolites of Aspergillus terreus and Suillus grevillei. Chem. Commun. 1975, 876. 

Total Synthesis of Pulvinones, 4-Benzylidene-2-phenyltetronic Acid Pigments... 

Ramage, R., G.J. Griffiths, F.E. Shutt, and J.N.A. Sweeney Dioxolanones as Synthetic Intermediates 2. Synthesis of Tetronic Acids and Pulvinones. J. Chem. Soc. (London) Perkin Trans. I 1984, 1539. 

The novel phosphonium salt (372) has been used in a non-stereoselective synthesis of members of the pulvinone group (373). This brief and useful method, which produces (E)-pulvinones for the first time, is complemented by an alternative approach to these compounds using a Dieckmann-type condensation of diester (374) to establish the tetronic acid... 

The group of 4-ylidenetetronic acid pigments known as pulvinones are closely related to the pulvinic acids and possess the general structure (60). It is interesting that pulvinones have only very recently been... 

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