Synthesis and crystal structure of (2 S ,4a R ,8a R )-6-oxo-2,4a,6,8a-tetra-hydro-pyrano[3,2- b ]pyran-2-carboxamide.

The pyran-opyran amide (2 S ,4a R ,8a R )-6-oxo-2,4a,6,8a-tetra-hydro-pyrano[3,2- b ]pyran-2-carboxamide, C ₉ H ₉ NO ₄ , 3 , was prepared by a chemoselective hydration of the corresponding nitrile, 2 , using a heterogeneous catalytic method based on copper(II) supported on mol-ecular sieves, in the presence of acetaldoxime. Compound 3 belongs to a new class of pyran-opyrans that possess anti-bacterial and phytotoxic activity. Crystallographic analysis of 3 shows a bent structure for the cis -fused bicyclic pyran-opyran, similar to nitrile 2 . Evidence of an intra-molecular hydrogen bond involving the amide group and ring oxygen was not observed; however, two separate inter-molecular hydrogen-bonding inter-actions were observed between the amide hydrogen atoms and adjacent carbonyl oxygen atoms along the b - and a -axis directions. The latter inter-action may also be supported by an inter-molecular 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 2 ₁ screw axis.
(© Greene et al. 2020.)