AmericanChemicalSociety.com

My laboratory has continued to study the preparation of unusual phosphorus ligands that are derived from chiral pyrylium salts.  We have studied the conversion of chiral phosphinine 2 to the corresponding phosphabarrelene (3) via reaction with benzyne made by a few different methods.  The phosphabarrelene, for which we have x-ray structural confirmation, exhibits remarkably upfield (+0.07 and -0.19 ppm) NMR signals for two of the protons (labeled a and b).  Optimization of the yield is proceeding. Coordination of this to transition metals, and preparation of bis-phosphabarrelenes is in progress.  Attempts to prepare chiral pyryliums (phosphinine precursors) from intermediate 1 have been thwarted by its low reactivity; under forcing conditions, any ketone enolates that can undergo aldol condensation do so in preference to the desired 1,4-addition.  We have found that substituting a CF₃ group for the C₆H₅ results in a more reactive intermediate, and we are pursuing new ligands on that basis.