Dynamic Chirality Control of tropos DPCB-digold Skeleton by Chiral Binaphthyldicarboxylate.

The planar 3,4-diphosphinidenecyclobutene (DPCB) can be remarkably twisted into a C2 -type helical structure by dual coordination of a AuCl moiety. A prompt chirality control of the twisted DPCB skeleton ligated by the digold units affords the enantiopure structure by exchanging the chloride ligands for chiral [1,1'-binaphthalene]-2,2'-dicarboxylate. The chirality of the diaurated 2,2'-bis(diphenylphosphanyl)-1,1'-biphenyl (BIPHEP) system can be controlled prior to that of DPCB. Mixing of a DPCB-bis(chlorogold) complex with the chiral silver salt dynamically leads to a single diastereomer, which was characterized by the (31) P NMR spectrum and the CD couplet patterns in the visible (DPCB) area. The absolute configuration of the singly induced helical structure was assigned by the theoretical CD spectra determined by TD-DFT calculations. Intramolecular alkoxycyclization of hexa-4,5-dien-1-ol catalyzed by the asymmetric DPCB-digold structure were also attempted.