ISSN:
0894-3230
Keywords:
Organic Chemistry
;
Physical Chemistry
Source:
Wiley InterScience Backfile Collection 1832-2000
Topics:
Chemistry and Pharmacology
,
Physics
Notes:
The synthesis of symmetrical blocked pyrylium derivatives by reaction of a cyclic aromatic ketone with ethyl orthoformate goes through an intermediate which can be isolated under certain conditions. This intermediate is unstable when starting from 1-tetralone derivatives but, surprisingly, it can be isolated easily when the synthesis is performed with 1-indanone derivatives. Further, in the latter case, this intermediate cyclizes hardly into the expected blocked pyrylium derivative. Its ionic structure was demonstrated by mass spectrometry and by 500 MHz 1H and 13C NMR techniques including heteronuclear H-C COSY and DEPT polarization transfer experiments. Hydrolysis of this intermediate in aqueous ethanol solution forms, in acidic or basic media, a pseudo-base, which in the latter case presents strong similarities with that obtained by the base-catalysed ring-opening of a blocked pyrylium ion. In both acidic and basic solutions, the pseudo-base obtained by the two sources shows identical UV-visible absorption spectra. The difficulty of the intermediate (g) originating from 1-indanone derivatives in cyclizing into the blocked pyrylium structure, in contrast to the intermediate formed from 1-tetralone derivatives, is tentatively explained.
Additional Material:
8 Ill.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1002/poc.610081106
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