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4‐Azapteridines. 2 . spectral, chromatographic, and X‐Ray crystallographic studies concerning the mode of covalent addition to the pyrazino[2,3‐ e ]‐ as ‐triazine ring system
Author(s) -
Tzeng CherngChyi,
Rychlewska Urszula,
Hodgson Derek J.,
Panzica Raymond P.
Publication year - 1986
Publication title -
journal of heterocyclic chemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.321
H-Index - 59
eISSN - 1943-5193
pISSN - 0022-152X
DOI - 10.1002/jhet.5570230108
Subject(s) - chemistry , adduct , ring (chemistry) , glyoxal , triazine , intramolecular force , solvent , stereochemistry , crystal structure , medicinal chemistry , crystallography , polymer chemistry , organic chemistry
The first examples of the unknown pyrazino[2,3‐ e ]‐ as ‐triazine ring system, that is, the 6,7‐dihydroxy‐5,6,7,8‐tetrahydropyrazino[2,3‐ e ]‐ as ‐triazines, have been prepared by ring closure of selected 5,6‐diamino‐ as ‐triazines with 40% aqueous glyoxal. These 4‐azapteridines experience a novel exchange process with alcohols at the C(7)‐position. When dissolved in alcohol and stirred at room temperature, the 7‐alkoxy, 6‐hydroxy analogues are formed and isolated. In fact, during ring closure, if alcohols are used as the solvent, only the latter compounds are obtained. Initially, cyclization of the ortho ‐diamino‐ as ‐triazines with glyoxal proceeds in a stereoselective manner giving rise to both the cis and trans adducts. A single‐crystal X‐ray diffraction study has determined the predominant and most stable adduct to be the trans (R,R or S,S) isomer. Spectroscopy (nmr) has verified the intermediacy of the cis adduct, but because of the aforementioned exchange process only the trans isomer is isolated. The site of exchange on these σ‐adducts has been rigorously established as C(7). A plausible reaction mechanism by which this exchange process occurs is presented.