Xanthylium salt

UV spectra, 3, 599 xanthone synthesis from, 3, 840 Xanthydryl chloride xanthone synthesis from, 3, 840 Xanthyletin synthesis, 3, 743, 804 Xanthylium laser dye synthesis, 3, 865 Xanthylium salts aromaticity, 3, 641 charge density calculations, 3, 576 C NMR, 3, 592 H NMR, 3, 585 mass spectra, 3, 620 reactions... 

Other xanthylium salt structures in which one of the catechin A-rings was substituted with an hydroxyl (in 6 or 8 position) or an ethylcarboxy group (in C8) were proposed on the basis of their NMR and MS data and postulated to result from condensation of the formylcatechin derivatives. Finally, carboxymethine-linked trimeric structures containing xanthylium and quinonoidal moieties were postulated for pigments showing absorbance maxima at 560 nm, on the basis of their mass signals at m/z 959 and 961 in the positive ion mode. ... 

Es-Safi, N.E. et al., Xanthylium salts formation involved in wine colour changes. Int. J. Food Sci. Technol. 35, 63, 2000. 

Es-Safi, N.E. et ah. Structure of a new xanthylium salt derivative. Tetrahedron Lett. 40, 5869,1999. Es-Safi, N.E. et ah, 2D NMR analysis for unambiguous structural elucidation of phenolic compounds formed through reaction between (-l-)-catechin and glyoxylic acid. Magn. Reson. Chem. 40, 693, 2002. 

Jurd, L. and Somers, T.C., The formation of xanthylium salts from proanthocyanidins. Phytochemistry 9, 419, 1970. 

Mass spectra of xanthylium salts have not been reported. However, elimination of a hydrogen radical from the molecular ion of 9//-xanthene gives a xanthylium cation as base peak which fragments further by loss of a -CHO radical (see Section 2.22.6.1). 

The site of addition of organometallic compounds (for examples, see Scheme 1) to pyrylium salts is dependent on the bulk of the alkyl group R of RMgX and on that of the substituents already present on the ring, but when the latter factor is unimportant, attack occurs at C-2 and the products tautomerize to the dienones. The reaction of methylmag-nesium iodide with a number of pyrylium salts has been studied (Scheme 2) (72BSF707). Xanthylium salts react only at C-9 and this suggests that the contribution of the alternative ion (50) is small. 

Treatment of diaryl ethers with dichloromethyl methyl ether in the presence of tin(lV) chloride leads to xanthylium salts (Scheme 268) (73JCS(Pl)ll04). It is necessary that the diaryl ether is so designed that electrophilic attack occurs ortho to the potential heteroatom. The thienopyrylium salts (673) and (674) have been prepared in the same manner. 

Similar processes have been observed with other aldehydes, such as glyoxylic acid. However, the carboxymethine-linked oligomers resulting from reaction with glyoxylic acid proceeded to xanthylium salts rather than to larger polymers (Es-Safi et al. 1999b). The postulated pathway involves dehydration and cyclisation of the carboxymethine dimer (Eig. 9B.6(4)) followed by oxidation of the resulting xanthene (Eig. 9B.6(5)) that was also detected in the medium. Formation of xanthylium salts was also shown in the case of furfural and hydroxymethylfurfural (Es-Safi et al. 2000). 

It was shown that benzo[fc]pyrylium salts 376 are capable also of recyclizations to produce the phenol derivatives 377 (equation 179). The 1,3-benzodioxanes 378 undergo an acid-induced fragmentation to xanthylium salts 380 via phenolic intermediate 379 (equation 180). 

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