Synthesis and crystal structure of (2S,4aR,8aR)-6-oxo-2,4a,6,8a-tetrahydropyrano[3,2-b]pyran-2-carboxamide

Abstract

The pyranopyran amide (2S,4aR,8aR)-6-oxo-2,4a,6,8a-tetrahydropyrano[3,2-b]pyran-2-carboxamide, C9H9NO4, 3, was prepared by a chemoselective hydration of the corresponding nitrile, 2, using a heterogeneous catalytic method based on copper(II) supported on molecular sieves, in the presence of acetaldoxime. Compound 3 belongs to a new class of pyranopyrans that possess antibacterial and phytotoxic activity. Crystallographic analysis of 3 shows a bent structure for the cis-fused bicyclic pyranopyran, similar to nitrile 2. Evidence of an intramolecular hydrogen bond involving the amide group and ring oxygen was not observed; however, two separate intermolecular hydrogen-bonding interactions were observed between the amide hydrogen atoms and adjacent carbonyl oxygen atoms along the b- and a-axis directions. The latter interaction may also be supported by an intermolecular C—H...O hydrogen bond. The lattice is filled out by close-packed layers of this hydrogen-bonded network along the c-axis direction, related from one to the next by a 21 screw axis.