Ferrocenyl oxazolines

Excellent enantioselectivity and double-bond regioselectivity can be achieved in an asymmetric Heck reaction between 2,3-dihydrofuran and aryl triflates by using a combination of chiral diphosphine-oxazoline ferrocenyl ligand and Pd catalyst <03CEJ3073>, as shown below. Chiral diphosphine-containing (arene)tricarbonylchromium(O) complexes were also used as ligands for this reaction to obtain the 2,3-isomer, however, both the yield and enantioselectivity were modest <03TA1455>. 

Scheme 11.16 Possible binding modes of the diphosphine oxazoline ferrocenyl ligands 31.

Tu, T., Deng, W.-R, Hou, X.-L. et al. (2003) The regioselectivity of the asymmetric intermolecular Heck reaction with planar chiral diphosphine-oxazoline ferrocenyl ligands. Chem. Eur. J., 9, 3073 1. 

Tu T, Hou X-L, Dai L-X (2003) Highly regio- and enantioselective Heck reaction of JV-methoxycarbonyl-2-pyrroline with planar chiral diphosphine-oxazoline ferrocenyl ligands. Org Lett 5 3651-3653... 

Donde Y, Overman LE (1999) High enantioselection in the rearrangement of allylic imidates with ferrocenyl oxazoline catalysts. J Am Chem Soc 121 2933-2934... 

In addition, Bonini et al. have shown that a planar chiral sulfur-containing ferrocenyl-oxazoline carbinol ligand, depicted in Scheme 3.59, could also be used to catalyse the addition of ZnEt2 to benzaldehyde with a moderate enantioselectivity (46% ee). ... 

Scheme 3.59 Sulfur-containing ferrocenyl-oxazoline carbinol ligand for addition of ZnEt2 to benzaldehyde.

The synthesis of ferrocene 9 relied on chemistry introduced by Sammakia, Uemura, and Richards [18]. They had shown that 2-ferrocenyl oxazoline 10 derived from t-leucine could be selectively deprotonated and trapped with electrophiles to afford ortho-functionalized planar-chiral products 11 with excellent diastereoselectivities (Scheme 2.1.2.3). Following this strategy, 9 became accessible in a highly straightforward manner by trapping the lithiated intermediate derived from 10 with benzophenone [10, 11],... 

Bolm found that chiral ferrocenyl hydroxy oxazoline 24 is also a good catalyst (88% ee). When the zinc species is prepared from a 1 2 mixture of diphenylzinc and diethylzinc, enantioselectivity is dramatically improved (97% ee) (Scheme 11) [36]. Extremely high enantioselectivity was also achieved by using planar chiral q5-cyclopentadienylrhenium tricarbonyl complex 25 [37]. 

Ferrocenyl ligands, via zinc reagents, 9, 120 Ferrocenylmethyl phosphonium salts, with gold(I), 2, 274 Ferrocenylmonophosphine, in styrene asymmetric hydrosilylation, 10, 817 Ferrocenyl oxazolines, synthesis, 6, 202 Ferrocenylphosphines with chromium carbonyls, 5, 219 in 1,3-diene asymmetric hydrosilylation, 10, 824-826 preparation, 6, 197 various complexes, 6, 201 Ferrocenylselenolates, preparation, 6, 188 Ferrocenyl-substituted anthracenes, preparation, 6, 189 Ferrocenyl terpyridyl compounds, phenyl-spaced, preparation 6, 188 Ferrocifens... 

Donde, Y., Overman, L. E. High Enantioselection in the Rearrangement of Allylic Imidates with Ferrocenyl Oxazoline Catalysts. J. Am. Chem. Soc. 1999, 121, 2933-2934. 

Various ferrocene-based organosilanols 165 have been synthesized in two steps fi om chiral 2-ferrocenyl oxazolines 163. Diastereoselective ortho-lithiation with sec-BuLi followed by electrophilic attack with chlorosilanes gave diastereomerically enriched 164, which were oxidized in air with [IrCl(C8Hi2)]2 as catalyst to give, after purification, stereochemically homogeneous samples of 165. Their application in asymmetric phenyl transfer reactions to substituted benzaldehydes afforded products with high ee (up to 91%) <050L1407>. 

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