Regioselective palladation of 2-oxazolinyl-[2.2]paracyclophanes.: Synthesis of planar-chiral phosphines

Palladations of the diastereomeric 4-(4-tert-butyl-2-oxazolinyl)-[2.2]paracyclophanes (S,Rp)-3 and (S,Sp)-3 have been investigated. Exclusive ortho-palladation occurs, when (S,Rp)-3 is treated with Pd(OAc)2 in glacial acetic acid. In contrast, (S,Sp)-3 affords products from either metallation in the ortho or the benzylic position of the [2.2]paracyclophane skeleton depending on the reaction conditions. Upon treatment of the resulting complexes with LiCl followed by addition of PPh3 mononuclear chloro{4-(2-oxazolinyl)-[2.2]paracyclophane,5-C,3-N}(triphenylphosphine)palladium(II) complexes (S,Sp)-7, (S,Rp)-7, and (S,Sp)-9 have been obtained. The solid state structures of (S,Sp)-7 and (S,Rp)-7 have been determined by X-ray diffraction analysis. Reaction of ortho-palladated complexes (S,Sp)-7 and (S,Rp)-7 with KPPh2 gives the corresponding planar-chiral phosphines (S,Sp)-11 and (S,Rp)-11, respectively. From benzyl substituted complex (S,Sp)-9 bromo derivative (S,Sp)-12 was obtained.