The preparation of trans-2,5-dialkylpyrrolidinylbenzyldiphenylphosphines:: new phosphinamine ligands for asymmetric catalysis

The preparation of new phosphinamine ligands 3a, 3b, possessing an enantiopure trans-2,5-dialkylpyrrolidinyl unit is described. Of the three synthetic approaches investigated, two proved successful with similar overall yields of 50-60%. One approach forms the trans-2,5-dialkylpyrrolidine unit first and then the diphenylphosphine is introduced whilst the other reverses the order of introduction. In each approach the key step is the cyclocondensation of an amine with an enantiopure, dialkyl-substituted 1,4-diol cyclic sulfate. An X-ray crystal structure of the palladium dichloride complex 13 of ligand 3a is presented. (C) 1998 Elsevier Science Ltd. All rights reserved.