Cyclopentanones, naturally occurring

Cycloheptatrienes, synthesis of 801 Cyclohexadienes 800, 801 Cyclohexanols, synthesis of 838 Cyclopentanones, naturally occurring 321 Cyclopentanone sulphoxides, reactions of 341... 

Currently 16 natural aflatoxins are known. Formulae 12-85 to 12-88 show the four major naturally occurring representatives of the B and G groups of aflatoxins, which are known as aflatoxins Bp B2, Gj and G2. The designation B (blue) or G (green) is associated with fluorescence of aflatoxins under UV light. While Aspergillus flavus produces mainly aflatoxins Bj and B2, contamination by A. parasiticus leads to aflatoxins Gj and G2 in the contaminated substrate. The basis of skeletons of aU aflatoxins is coumarin condensed with bisdihydrofurofuran (dihydrobisfuran) and cyclopentanone in the first two aflatoxins, while the other two substances contain 5,6-dihydropyran-2-one instead of cyclopentanone. 

A wide range of donor ketones, including acetone, butanone, 2-pentanone, cyclopentanone, cyclohexanone, hydroxyacetone, and fluoroacetone with an equally wide range of acceptor aromatic and aliphatic aldehydes were shown to serve as substrates for the antibody-catalyzed aldol addition reactions (Chart 2, Table 8B2.6). It is interesting to note that the aldol addition reactions of functionalized ketones such as hydroxyacetone occurs regioselectively at the site of functionaliztion to give a-substitutcd-fi-hydroxy ketones. The nature of the electrophilic and nucleophilic substrates utilized in this process as well as the reaction conditions complement those that are used in transition-metal and enzymatic catalysis. 

The unusual pentacyclic system of (+)-pentacycloanammoxic acid (1) was created in 21 steps with an overall yield of 2%. The stereochemistry of the target was established relatively late in this convergent synthesis by a novel diastereoselective de Mayo reaction using the chiral cyclopentanone 7. Determination of the absolute configuration of (+)-l was accomplished in the course of the total synthesis by X-ray diffraction of the a,P-unsaturated ketone 25. Although many photochemical transformations occur in this total synthesis, the authors are in doubt about the involvement of photochemical processes in the biosynthesis of 1, as the natural environment of C. B. anammoxidans is dark and anaerobic. 

Another study " used a highly modified stilbene derivative (host M in Figure 22) as the host structure in a set of solid inclusion compounds containing a variety of small guest molecules (acetone, cyclopentanone, y-butyrolactone, dioxane, dimethylsulfoxide, pyridine, and A,A-dimethlyformamide), and it was observed that unidirectional cis trans photoisomerization occurs for the stilbene derivative. However, this one-way photoisomerization also occurs for the same stilbene derivative in the solid state (in the absence of any guest molecules), so the unidirectional nature of the photoisomerization reaction in this case is not dependent on the inclusion phenomenon, although it does provide an interesting point of comparison. 

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