Pergamon Tetrahedron: Asyrametry, Vol.8, No. 8, pp. 1179-1185, 1997 (~) 1997 ElsevierScienceLtd. All rights reserved. Printed in GreatBritain PII: S0957..4166(97)00104-3 0957-4166/97 $17.00 + 0.00 Pd-Catalyzed asymmetric allylic alkylations using various diphenylphosphino(oxazolinyl)ferrocene ligands Kyo Han Ahn*,* Chang-Woo Cho, Jaiwook Park* and Sunwoo Lee Department of Chemistry and Center for Biofunctional Molecules, Pohang University of Science and Technology (POSTECH), San 31 Hyoja-dong, Pohang 790-784, Korea Abstract: Pd-Catalyzed asymmetric allylic alkylations have been studied using a series of chiral diphenylphosphino(oxazolinyl)ferrocene ligands 4-8. With these ligands, up to 99% and 63% ee are Obtained for rac-(E)-l,3-diphenylprop-2-enyl-l-acetate and rac-(E)-l,3- dimethylprop-2-enyl-l-acetate, respectively, with dimethyl malonate as the nucleophile. Some of the ligands 4-6 generate corresponding Pd-catalysts more reactive than those formed from other known ligands. A noticeable influence of the planar chirality on the enantioselectivity is observed. Different coordination modes can be suggested for the distinguishable enantioselectivity and reactivity patterns observed in the reactions with the ligands 4-8. (~) 1997 Elsevier Science Ltd The Pd-catalyzed asymmetric allylic substitution reaction I has been demonstrated to be useful in the syntheses of valuable small molecules and complex natural products. 2 A variety of chiral ligands have been studied in the Pd-catalyzed allylic substitutions. 3 Much effort has been made to elucidate crucial factors for the enantioselection of the reaction. 4 With a few exceptions, 2g one set of chiral ligands that produces high selectivity for acyclic allylic acetates, usually shows greatly decreased selectivity for cyclic substrates, and vice versa. Furthermore, for given acetates, the steric bulkiness of the acetate dramatically alters the enantioselectivity.3p Therefore, the search for the best ligand for the catalysis may be dependent on the type and steric bulkiness of allylic substrates. A recent introduction of 'hetero-chelates' such as (phosphinoaryl)oxazoline ligands 1 opened up a path to the development of other kinds of hetero-chelates. 3p-r These N,P-chelates, a hybrid of the previously known oxazoline and phosphine ligands, are demonstrated to be efficient in the Pd-catalyzed allylic substitution and other catalytic reactions. 5 Of particular interest is that these ligands generate more reactive Pd-catalysts than most of the known N,N- and P,P-chelates, seemingly owing to the 'trans effect'.6 Recently we and others have developed a highly diastereoselective lithiation of oxazolinylfer- rocene compounds, 7 and we have synthesized a variety of diphenylphosphino(oxazolinyl)ferrocene compounds (DPOF 2-8) which would be potentially useful ligands for organometaUic catalysts. 8 A number of ferrocene-based P,P-chelates have been successfully utilized in the transition metal- catalyzed asymmetric reactions, 9 and recently the application of ferrocene-based N,P-chelates for asymmetric catalysts is attracting interest. 1° Here we report the Pd-catalyzed allylic alkylation with DPOF ligands 4--8. Since these ligands have different planar chiralities, it is of interest to study their effects on the enantioselectivity. In addition, it is an intriguing question which chelation modes among several possible combinations would operate in the substitution reaction. * Corresponding author. Email: ahn@vision.postech.ac.kr 1179