Ylidenetetronic Acids

Formulation (43) shows the basic pulvinic acid carbon skeleton, and all known natural pulvinic acids show variations which include either hydroxylation of methoxylation of the benzene rings or lactonisations involving the carboxy function (Table 2). In addition, a few methyl ester and amide derivatives of the acids occur naturally. Early studies of the constitutions of pulvinic acids found in lichens have been summarized by Dean (7), and a useful account of pigments found in mushrooms, which includes pulvinic acid pigments, has been presented recently by Steglich 47). 

Lepraria, Evernia, Centraria, Cyphe-lium, Calycium and Parmelia species of Lichen (7). 

Sticta, Candelaria Gyalolechia, Lepraria, Gasparrima, Physcia, Chrysothrix and Callopsima species of Lichen (7,50). 

Several Boletus species (55) Xerocomus chrysenteron (56) Gomphidius glutino-sus (57) Rhizopogen roseolus (5 ). 

Suillus piperatus 60) Rhizopogon roseolus (55) Boletus rubel-lus 62). 

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IR spectra, 3, 596 occurrence, 3, 689 4-Ylidenebutenolides occurrence, 4, 696 4-Ylidenetetronic acid synthesis, 4, 696 Ylides... 

Extensive studies on the synthesis of 4-ylidenetetronic acids conducted by Pattenden and his colleagues have been based mainly upon furan-2,5-diones (maleic anhydrides) in which a carbonyl reacts selectively. Unexpectedly, metal hydride attacks both carbonyl groups about equally in the methyl derivative, but in the methoxyfuran-2,5-diones, where electron release from the methoxy group greatly reduces the activity of the distal carbonyl group,... 

Natural 4-ylidenebutenolides and 4-ylidenetetronic acids , Pattenden, G., Prog. Chem. Org. Nat. Prod., 1978, 35, 133. 

Pattenden, G. Natural 4-Ylidenebutenolides and 4-Ylidenetetronic Acids. Fortschr. Chem. organ. Naturstoffe 35, 133 (1978). 

Ylidenebutenolides and 4-ylidenetetronic acids comprise a group of natural products many members of which have been discovered only in the past decade. The term butenolide describes the unsaturated... 

The rapid expansion in the number of structurally novel 4-ylidene-butenolides and 4-ylidenetetronic acids since 1962, many displaying interesting biological properties, has prompted considerable activity into the chemical synthesis and biosynthesis of these metabolites. This review aims to reflect the structure and distribution of natural 4-ylidenebutenolides and 4-ylidenetetronic acids and to discuss developments in their chemical synthesis and biosynthesis. 

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... 

A small group of novel 4-ylidenetetronic acid derivatives has been isolated from Penicillium species. The first of these to be discovered was dehydrocarolic acid from P. drierascens Biourge in 1947 80). The struc-... 

In general terms, two broadly based approaches towards the synthesis of 4-ylidenebutenolides and 4-ylidenetetronic acids can be discerned. The first of these approaches involves, as a key stage, the intramolecular cyclisation of an acyclic precursor molecule, frequently in the form of a 4-oxo-2-enoic acid (viz 89) or a Z-2-en-4-ynoic acid (viz 90) (Scheme 3). 

Scheme 3. Synthetic approaches to 4-ylidenebutenolides and 4-ylidenetetronic acids...

Aldol-type condensations between but-2-enolides and carbonyl compounds constitute probably the most flexible routes to 4-ylidene-butenolides and 4-ylidenetetronic acids. One of the first applications of this general approach was in the preparation of (130) from but-2-enolide (129 a) employing aqueous sodium hydrogen carbonate as base 114). Bohlmann and Zdero 34) later described a synthesis of the naturally occurring thiophene (131) involving condensation between butenolide (129 b) and 5-methylthiophene-2-aldehyde in the presence of piperidine acetate in glacial acetic acid at 80°. 

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