Enantioselective Preparation of C2-Symmetrical Ferrocenyl Ligands for Asymmetric Catalysis

Abstract

Corey ± Bakshi ± Shibata (CBS) reduction of the 1,1'-diacylmetallocenes 5 and 7 provides the C 2 -symmetrical diols 4 and 10, which proved to be useful starting materials for stereocontrolled ligand synthesis. Diols 4 and 10 can be easily converted to a wide range of diamines, diphosphines, and dithioacetates by nucleophilic substitution of the hydroxyl function with full retention of configuration. Furthermore, the aminophosphines 30 and 31 become easily accessible. Compounds 30 and 31 have been used as ligands in enantioselective cross-coupling of racemic secondary Grignard reagents with vinyl bromides. A selectivity up to 93 % ee could be reached for the first time in the preparation of (S)-(E)-1,3-diphenyl-1-butene (34 b), which was transformed into the enantiomerically pure chiral building block 37 with a pseudoasymmetric center in a straightforward, threestep synthesis.

Symmetrical 1,1′‐Bidentate Ferrocenyl Ligands

“…The Pd-complex of L-17c catalyzed the asymmetric cross-coupling of 1-phenylethylmagnesium chloride and b-bromostyrene providing (S)-1,3-diphenyl-1-butene with up to 93% ee. The details are summarized in Table 7.4 [41].…”

“…These ligands were applied in the Pd-catalyzed asymmetric cross-coupling of 1-phenylethylmagnesium chloride with vinyl bromide or b-bromostyrene with moderate yield (82%) and enantioselectivity (68% ee) [41,42].…”

Industrial Catalysts for Regio‐ or Stereo‐Selective Oxidations and Reductions. A Review of Key Technologies and Targets

“…The original catalyst and reagent system [diphenyl prolinol/methane boronic acid (R)] is known as the Corey-Bakshi-Shibata (CBS) [45] reagent. Numerous examples describing the application of this method are known, as exemplified by the synthesis of the chiral ferrocene bis-alcohol needed for ligand synthesis described by Schwink and Knochel [46] (Figure 1.38). Although very good enantio-and diastereoselectivities were achieved, high catalyst loadings were required.…”

Diastereoselective 1,2-Addition of Organometallic Reagents to Chiral Formylferrocenes Leading to Enantiomerically Pure Ferrocenyl Amino Alcohols: Application to Asymmetric Dialkylzinc Addition to Aldehydes and Synthesis of Optically Active 1,2-Homodisubstituted Ferrocenes

“…[7] We are also interested in 1,2-ferrocenediol as another new chiral ligand, which may be prepared through retentive α-substitution of 6a and/or 13 by acetate. The ferrocenyl amino alcohol (1S,2S,2Sp)-13 was prepared in good overall yield (68%) by stereoselective methylation of 4 with dimethylzinc followed by desilylation.…”

“…The C 2 -symmetrical 1,1Ј-ferrocenediol is obtained from asymmetric reduction of 1,1Ј-diacyl ferrocene and can be converted into the corresponding ferrocenediamine and -diphosphane derivatives. [7] The planar chiral ferrocene can ity and the chirality of the diastereomeric ferrocenes. Alkylation with 2, 3, and 6a gave (1R)-phenyl-1-propanol in good yields with high ee values (87−91% ee).…”