Stereodivergent Synthesis of Two Novel α‐Aminophosphonic Acids Characterised by a cis‐Fused Octahydroindole System

The synthesis of two new α-aminophosphonic acids, namely (2S*,3aS*,7aS*)- and (2R*,3aS*,7aS*)-octahydroindole-2-phosphonic acids, is described. They are analogues of phosphoproline with a cyclohexane ring fused to the pyrrolidine moiety. The ring junction has cis stereochemistry in both cases, but the two compounds differ in the relative orientation of the cyclohexane and phosphonate moieties. The two amino acids were prepared from a common starting material following stereodivergent routes that provide the desired stereoisomer with complete stereocontrol. The relative configurations of the compounds synthesised were confirmed by X-ray diffraction analysis.