Naturally Occurring Furan Derivatives

The intramolecular Diels-Alder methodology has been used in approaches to naturally occuring furan derivatives (93JCS(Pl)2395). For example, thermolysis of (311) gave the product (312) in almost quantitative yield by cyclization followed by isomerization of the exocyclic double bond to rearomatize the furan residue. The reaction proved to be highly stereoselective. 

Naturally Occurring Furan Derivatives The mass spectra of naturally occurring oxygen heterocyclics were reviewed only recently.52... 

The following table contains those naturally occurring furan derivatives which have recently been found, isolated, or elucidated. The name, origin, and structure are given in each case, and the references are kept to a minimum. 

There are large numbers of naturally occurring representatives, especially of pyrrole that include the important polypyrroles (porphyrins and corrins), and the nitropyrrole antibiotics such as pyr-rolomycins and pyrroxamycin. Derivatives of furan have been used as fungicides and A-vinylpyr-rolidone is an important monomer for the production of blood plasma extenders and for cosmetic applications. On account of the similarity in the pathways for the aerobic degradation of monocyclic furan, thiophene, and pyrrole, all of them are considered here. Anaerobic degradation of furans is discussed in Part 2 of this chapter. 

The chemistry of fiiians and benzofurans was a Held of lively research in the last year. There are a number of reasons for this activity. The furan ring system - both in its native as well as in its reduced form - occurs in a great number of natural products and a wide variety of these compounds has been isolated from natural sources. This subject is treated regularly with care and accuracy in Heterocycles and will not be repeated here. Therefore only a few examples will be given in this chapter. Several new furan derivatives were isolated from natural sources (-)-wistarin 1 from the marine sponge Ircinia sp. <99TA3869>,... 

The commonest five-membered heteroaromatic compounds containing one heteroatom are pyrrole (30), furan (31) and thiophene (32). Their substituted derivatives and the substituted derivatives of the corresponding benzo analogues [indole (33), benzofuran (34) and benzothiophene (35)] are widespread naturally-occurring compounds. 

Psoralens, also known as furocoumarins, are naturally occurring or synthetic tricyclic aromatic compounds and are derived from the condensation of a coumarin nucleus with a furan ring [1-10]. Several new furocoumarins have been isolated from natural sources [10, llj. In addition, the synthetic methods for production of these molecules have been described and reviewed [10]. The synthetic methods can be organized on the basis of the key step used for the formation of the two different oxygenated rings, hi this respect, there are three possibilities (i) formation of the furan ring onto the coumarin, (ii) formation of the pyrone ring onto the benzofuran and... 

---