AN UNEXPECTED INTERMEDIATE IN THE SYNTHESIS OF SUBSTITUTED PYRIDONES

The title compound, -1,2,3,7,8,8a-hexahydroimidazo[1,2-a]pyridin-7-one (I), is a novel cyclic intermediate in the synthesis of 1-(2-amino-et hyl)-3-hydroxy-2-methyl-4(1H)-pyridon (II), a well known Fe-III chelat or, following a standard route for the synthesis of substituted pyrido nes. Compound (I) is the major solid intermediate in this reaction and its structural identity has been established conclusively by single-c rystal X-ray crystallography. It is a monohydrate in the solid state, C15H18N2O2.H2O, and it is obtained upon trituration of the colored oil obtained from the reaction of ethylenediamine with 3-benzyloxy-2-meth yl-4-pyrone. Each water molecule bridges two molecules of (I), hydroge n bonding with the carbonyl O atom of one molecule [O ... OW 2.796(4) Angstrom] acid with the N atom of the other [N ... OW 2.903 (4) Angstr om]. The methyl group at the bridgehead is axially located in a trans position with respect to the bulky benzyloxy group. The pyridone ring assumes a slightly distorted half-chair conformation.