Synthesis of 1,3-Bis(diphenylphosphinoyl)alkanes via Double Addition of Diphenylphosphine to α,β-Unsaturated Carbonyl Compounds: Sequential 1,4- and 1,2-Addition Promoted by NbCl₅-BF₃·OEt₂

Lewis acid-promoted double addition of diphenylphosphine to various α,β-unsaturated aldehydes and ketones is described. By utilizing niobium(V) chloride and diethyl etherboron trifluoride complex (stoichiometric), the reaction provides the monooxides of 1,3-bis(diphenylphosphino)alkane, which were oxidatively worked up to yield the corresponding bisoxides 1-6 in high yields. The reaction of diphenylphosphine with 2-cyclohexenone afforded trans-1,3-bis(diphenylphosphinoyl)-cyclohexane (6) as the sole isolable product. The relative stereochemistry of 6 was rigorously determined by X-ray crystallography.