PREPARATION OF [5+6]-BICYCLIC, [6+6]-BICYCLIC, AND [6+7]-BICYCLIC GUANIDINES FROM C,C'-BIS(IMINOPHOSPHORANES)

A one-pot synthesis of [5 + 6]-, [6 + 6]-, and [6 + 7]-rigid bicyclic guanidines (6, 8, 19, 21, 23) based on a bis(iminophasphorane)-mediated annulation strategy is reported. The crystal and molecular structure of the parent [5 + 6]-bicyclic guanidine 8 has been established by X-ray diffraction. The crystallographically independent molecule forms dimers through a centre of symmetry by N-H...N hydrogen bonds. The molecule, and therefore the dimer, is statistically disordered in a 65/35 ratio. A statistical study of N-H...N hydrogen bonds of this kind of dimers has been carried out by using the Cambridge Structural Database.