Synthesis and conformational analysis of 1,3,2-diazaphosphorino[6,1-a]isoquinolines, a new ring system

Through ring-closure reactions of N- or 1′-substituted 1-(2′-aminoethyl)-6,7-dimethoxy-1,2,3,4-tetrahydroisoquinolines () with phenylphosphonyl dichloride, 1- or 3-substituted 4-phenyl-1,3,4,6,7,11b-tetrahydro-2H-1,3,2-diazaphosphorino[6,1-a]isoquinolin-4-one diastereomers ( and ), the first representatives of a new ring system, were prepared. The diastereomeric ratios in the cyclizations and the conformer () populations of the nitrogen-bridged tricyclic systems ( and ) were strongly influenced by the N- and 1′-substituents of the starting diamines. The conformational analysis of compounds and was performed by 1H, 13C and 31P NMR methods.