~ ) Pergamon Tetrahedron: Asymmetry, Vol. 8, No. 24, pp. 4027-4031, 1997 © 1997 Elsevier Science Ltd. All rights reserved. Printed in Great Britain PII: S0957-4166(9"/)00554-5 0957-4166/97 $17.00 + 0.00 A new C2-symmetric chiral bisphosphine ligand containing a bioxazole backbone: highly enantioselective hydrosilylation of ketones Sang-gi Lee,* Chung Woo Lim, Choong Eui Song and In O Kim Division of Applied Science, Korea Institute of Science and Technology, P.O. Box 131, Cheongryang, Seoul 130-650, Korea Abstract: C2-Symmetric (4S,4' S)-2,2'-bis(o-diphenylphosphinophenyl)-4,4' ,5,5'-tetra- hydro-4,4'-bi(l,3-oxazole) (1, Phos-Biox) has been designed and synthesized as a chiral ligand for metal-catalyzed reactions. The Phos-Biox 1 was found to be an efficient ligand for rhodium(I)-catalyzed asymmetric reduction of prochiral acetophenones with diphenylsilane to give optically active secondary alcohols of up to 97% ee. © 1997 Elsevier Science Ltd. All rights reserved. The design and synthesis of new chiral ligands for transition metals have played a significant role in the development of catalytic asymmetric reactions, and there have been many efforts devoted to the preparation of efficient ligands. 1 In particular, to reduce the number of stereochemical permutations within the catalytic ensemble, a series of C2-symmetric chiral bisphosphine (P,P- chelation) 2 and bisoxazoline (N,N-chelation) 3 ligands have attracted considerable attention as chiral ligands for metal-catalyzed asymmetric reactions. Recently, an introduction of phosphine-oxazoline hybrid ligands opened up a new path to the development of chiral ligands, and are demonstrated to be efficient in various metal-catalyzed asymmetric reactions. 4 However, in sharp contrast with the P,P- and N,N-ligands, C2-symmetric phosphine-oxazoline hybrid ligands have not received much attention: During our studies on the design of new C2-symmetric bioxazole (Biox) derivatives as chiral ligands, 6 we have prepared optically active C2-symmetric bisphosphine ligand, (4S,4'S)-2,2'- bis(o-diphenylphosphinophenyl)-4,4',5,5'-tetrahydro-4,4'-bi(1,3-oxazole) 1 (abbreviated (S,S)-Phos- Biox) which is expected to be effective as a chiral ligand for several types of transition metal- catalyzed asymmetric reactions. Here we report the results of its application in rhodium(I)-catalyzed enantioselective hydrosilylation of acetophenone derivatives. o J-;. /r-- O ~.//'-R Rr~ 1 : R =PPh2 (S,~-Phos-Biox 2 : R = F (S,S)-F-Biox 3 : R = H (S,S)-Ph-Bio× The key feature of this bisphosphine ligand is that the conformationally rigid chiral bioxazole ring can restrict the flexibility of the ligand bound to a transition metal. Thus, the chiralities of the backbone could be transferred efficiently to the phosphine. Moreover, this ligand may provide a wide bite angle for the metal chelation, and create a deep chiral pocket. The C2-symmetric bisphosphine-bioxazole hybrid ligand 1 was readily synthesized by the reaction of the potassium diphenylphosphide with fluorobioxazole 2 which was prepared according to our previously reported method using o-fluorobenzoyl chloride instead of benzoyl chloride for Ph-Biox 3. 6 * Corresponding author. Email: 13712@kistmail.kist.re.kr 4027