Of chalcones

Treatment of 2-isoxazolines with acid usually leads to ring rupture and formation of chalcone products 62HC(l7)l), although 5-methyl-3-phenyl-2-isoxazoline forms a quaternary salt with dimethyl sulfate in the presence of perchloric acid (Scheme 51) (73BSF1390). 

Anindeno[1.2-6]pyrylium (123) has been reported to result from the autocondensation of chalcone (FeCls-f Ac20). ... 

The use of the bisoxazolinylanthracene ligand AnBOX in an Evans-like aziridination of chalcones has thrown up the interesting observation that the sense of enantiodiscrimination is inverted in relation to the reaction carried out with a traditional BOX ligand with similar stereogenicity (Scheme 4.17) [16]. 

D.N. Dhar, The Chemistry of Chalcones and Related Compounds Wiley-Interscience New York, (1981). 

Lawton, M.A., Dixon, R.A., Rowell, P.M., Bailey, J.A. Lamb, C.J. (1983). Rapid induction of the synthesis of phenylalanine ammonia-lyase and of chalcone synthase in elicitor-treated plant cells. European Journal of Biochemistry, 129, 593-601. 

Scheme 20), these acetals could readily be converted into isofiavones. Unfortunately, very low yields of rearrangement products were obtained using thallium(III) acetate, and separation and purification of acetals such as (XXXIV) was extremely tedious. Reaction of chalcones with TTN, on the other hand, is generally complete within a few hours at room temperature 95), and Farkas et al. (J75) have developed the Ollis procedure into a simple method for the preparation of isofiavones (Scheme 21). 

Oxidation of chalcones with TTN has been studied in detail (95, 96), and it has been shown that the products obtained depend on the amount of reagent and the solvent employed. Oxidation with 1 equivalent of TTN in methanol, methanol-chloroform, or methanol-boron trifluoride leads to acetals of the type (XXXIV) (see also Scheme 21) in yields of 20-80%. When 3 equivalents of TTN are employed, however, and aqueous glyme containing a little perchloric acid used as solvent, the products are benzils. This remarkable transformation, which proceeds in yields varying from moderate to good (40-80%), involves three distinct oxidations by TTN, and these are outlined in Scheme 22. Each individual step in this reaction sequence has been investigated in detail, with the result that useful procedures have been developed for the oxidation of both deoxybenzoins and benzoins to benzils with TTN (96). 

These conclusions were supported by the results obtained in a study of the reactions of various types of acetylenes with TTN (94). Hydration of the C=C bond was found to occur to a very minor extent, if at all, with almost all of the compounds studied, and the nature of the products formed was dependent on the structure of the acetylene and the solvent employed. Oxidation of diarylacetylenes with two equivalents of TTN in either aqueous acidic glyme or methanol as solvent resulted in smooth high yield conversion into the corresponding benzils (Scheme 23). The mechanism of this oxidation in aqueous medium most probably involves oxythallation of the acetylene, ketonization of the initially formed adduct (XXXV) to give the monoalkylthallium(III) derivative (XXXVI), and conversion of this intermediate into a benzoin (XXXVII) by a Type 1 process. Oxidation of (XXXVII) to the benzil (XXXVIII) by the second equivalent of reagent would then proceed in exactly the same manner as described for the oxidation of chalcones, deoxybenzoins, and benzoins to benzils by TTN. The mechanism of oxidation in methanol solution is somewhat more complex and has not yet been fully elucidated. 

It is interesting to note that condensation of the N,N-bis(silylated) enamine 538 with a variety of chalcones such as benzalacetophenone 735 proceeds, via 539 and subsequent cyclization and oxidation, to pyridines such as 540 [106, 108] whereas persilylated co-amino ketones such as the 2-substituted pyridine 541 cyclize, via 542, in 29% yield, to the pyrrole 543 [109] (Scheme 5.36). 

B. Waiczak, L. Morin-Allory, M. Chrdtien, M. Lafosse and M. Dreux, Factor analysis and experiment design in high-performance liquid chromatography. III. Influence of mobile phase modifications on the selectivity of chalcones on a diol stationary phase. Chemom. Intell. Lab. Syst., I (1986) 79-90. 

There is a continual interest in the UV spectra of chalcone analogs of type 4, where R may be the selenienyl moiety.19 The IR spectra of these compounds have also been measured in the solid state and in solutions of carbon tetrachloride and chloroform.20 The interaction between the ring and the... 

Figure 3.6. Synthesis of chalcone, flavanone, and stilbene from p-coumaric and malonic acids.

Bomati EK, Austin MB, Bowman ME, Dixon RA and Noel IP. 2005. Structural elucidation of chalcone reductase and implications for deoxychalcone biosynthesis. J Biol Chem 280 30496-30503. 

A novel one-step synthesis of thiazolo[3,2-fc]l,2,4-triazoles 182 was reported from the reaction of chalcones 180 with bis(l,2,4-triazolyl)sulfoxide 181 . 1,2,4-... 

Chalcones (including 11) contain a l,3-diaryl-a,/)-unsaturated ketone moiety and have anti-cancer properties [38]. As analogs of CA-4, 7, the mode of cytotoxic action of chalcones has been shown to be similar to the com-bretastatins. They bind to the colchicine site of tubulin and inhibit tubulin polymerization [39]. 

This section has illustrated a number of chalcone-derived analogs of com-bretastatins. For the most part there have been limited biological studies with these compounds however, the synthesis was included for completeness and to indicate that they warrant further investigation. 

JEZ, J.M., BOWMAN, M.E., DIXON, R.A., NOEL, J.P., Structure and mechanism of chalcone isomerase an evolutionarily unique enzyme in plants, Nature Struct. Biol., 2000, 7,786-791. 

CAIN, C.C., SASLOWSKY, D.E., WALKER, R.A., SHIRLEY, B.W., Expression of chalcone synthase and chalcone isomerase proteins in Arabidopsis seedlings, Plant Mol. Biol., 1997, 35,377-381. 

---