NOVEL REACTION OF AMINOPYRIDINES WITH GLYOXAL AND FORMALDEHYDE - SYNTHESIS OF 4,8-DI(N-AMINOPYRIDYL)2,6-DIOXA 4,8-DIAZABICYCLO[3.3.0]OCTANE, 6,8-DI(N-AMINOPYRIDYL)2,4-DIOXA 6,8-DIAZABICYCLO[3.3.0]OCTANE AND X-RAY STRUCTURAL STUDY OF RELATED 1,3-DI(N-AMINOPYRIDYL)4,5-DIHYDROXY IMIDAZOLIDINE

Condensation of 2-aminopyridine with glyoxal proceeds with high select ivity to a mixture of meso and dl diol 7 to be easily transformed into the corresponding bicyclooctane 2a and 3a with formaldehyde and aceto nitrile as solvent. In water, however, the reaction selectively produc es imidazolidine 4a. Based on NMR analysis, the major diastereomers we re assigned as syn derivatives. X-ray crystal structure of 4a shows a planar configuration for imidazolidine ring, in line with two anomeric effects, first a strong n(N) --> sigma(C-O) interaction and second a weak n(O) --> sigma(C-N) one. A network of hydrogen bonding between pyridyl nitrogens and hydroxy hydrogens forms a pattern of twelve atom in a chair-like conformation. (C) 1997, Elsevier Science Ltd.