X-ray diffraction analysis of two hexahydropyrido[2,1-b][1,3,4]oxadiazines: evidence for the effect of steric congestion on anion formation at the aminonitrile centre

Abstract

The X-ray crystal structures of (2R,3S,6R,9aS)- and (2S,3S,6R,9aR)-3,4-dimethyl-2-phenyl-3,4,7,8,9,9a-hexahydro-2H,6H-pyrido[2,1-b][1,3,4]oxadiazine-6-carbonitrile, (6) and (7), respectively, revealed that the six-membered rings are chair shaped and the ring junctions are cis. Futhermore, it was found that the C6 H atom is hindered by the axial methyl group substituted at C3 in (6) and that the C6 H atom in compound (7) is similarly protected by the presence of the equatorial methyl group on N4. These results provide insight into the reactivity of these molecules