Synthesis and characterization of 1,9-difluoro-5-methyl-5-phenyl-10,11-dihydro-5 H-dibenzo[b,f]silepin

Abstract

The synthesis of 2,2′-difluoro-6,6′-dichlorobibenzyl, a precursor to dibenzometallepins, has been accomplished from bromination of 2-chloro-6-toluene followed by coupling of the benzyl bromide produced with PhLi. A variety of conditions were studied for conversion to a diGrignard reagent the most successful of which involved activated magnetism (Mg ∗) produced from reduction of MgBr 2 and K. Reaction of the diGrignard with PhMeSiCl 2 produced 1,9-difluoro-5-methyl-5-phenyl-10,11-dihydro-5 H-dibenzo[b,f]silepin ( 3a). The silepin was characterized by an X-ray crystal structure in the solid state and in solution by 1H, 13C, 29Si and 19F NMR spectroscopy. The solid structure reveals a folded boat conformation for the central seven-membered ring and a butterfly angle for the tricyclic framework of 124°. The 1H NMR data in solution exhibits a complex, unsymmetrical multiplet associated with the ethano-bridge protons. The conformations of 3a were generated by MM2 calculations and the results demonstrated that there were four enantiomeric pairs of similar energy. The configuration with an axially oriented phenyl group corresponded closely to the configuration observed in the solid state. energy. The configuration with an axially oriented phenyl group corresponded closely to the configuration observed in the solid state.