Enantioselective Brunner

Brunner H. Right or Left in Chemistry - Enantioselective Catalysis With Transition Metal Compounds Quim. Nova 1995 18 603 07... 

Brunner H. Right or Left-that is the Question-Enantioselective Catalysis with Transition Metal Compounds in Adv. Catal. Des., Proc. Workshop, 2nd. 1993 245, Ed. Graziani M., Rao C. N. R., Pb. Wordl Sci. Singapore... 

Brunner H. Enantioselective Catalysis With Transition Metal Componnds. Right or Left - This Is the Qnestion Adv. Chem. Ser. 1992 230 143-152 Keywords homo-Diels-Alder reaction of norbornadiene... 

Brunner et al. attached chiral branches to non-chiral catalytically active sites. With the aim to influence the enantioselectivity of transition metal catalyzed reactions they synthesized several dendritically enlarged diphosphines such as 81 [101] (Fig. 29). In situ prepared catalysts from [Rh(cod)Cl]2and81 have been tested in the hydrogenation of (a)-N-acetamidocinnamic acid. After 20 hours at 20 bar H2-pressure (Rh/substrate ratio 1 50) the desired product was obtained with an enantiomer ratio of 51 49. 

Brunner, H. Zettlmeier, W. Handbook of Enantioselective Catalysis with Transition Metal Compounds VCH Wein-heim, Germany, 1993 Vols. I and II. 

Brunner, H., Enantioselective Synthesis of Organic Compounds with Optically Active Transition Metal Catalysts in Substoichiometric Quantities, 18, 129. 

Brunner, Leitner and others have reported the enantioselective transfer hydrogenation of alpha-, beta-unsaturated alkenes of the acrylate type [50]. The catalysts are usually rhodium phosphine-based and the reductant is formic acid or salts. The rates of reduction of alkenes using rhodium and iridium diamine complexes is modest [87]. An example of this reaction is shown in Figure 35.8. Williams has shown the transfer hydrogenation of alkenes such as indene and styrene using IPA [88]. 

Barton et al. (92) discovered that the monophenylation of diols using triarylbis-muth reagents may be catalyzed by Cu(II) salts. Brunner has examined various ligands in this reaction and found that modest enantioselectivities are observed in the... 

Brunner et al. [26] synthesized and applied so-called dendrizymes in enan-tioselective catalysis. These catalysts are based on dendrimers which have a functionalized periphery that carries chiral subunits, (e.g. dendrons functionalized with chiral menthol or borneol ligands). The core phosphine donor atoms can be complexed to (transition) metal salts. The resultant dendron-enlarged 1,2-diphosphino-ethane (e.g. 16, see Scheme 17) Rh1 complexes were used as catalysts in the hydrogenation of acetamidocinnamic acid to yield iV-acetyl-phenylalanine (Scheme 17) [26]. A small retardation of the hydrogenation of the substrate was encountered, pointing to an effect of the meta-positioned dendron substituents. No significantly enantiomerically enriched products were isolated. However, a somewhat improved enantioselectivity (up to 10-11% e.e.) was... 

Chiral carboxylates such as a-phenylcarboxylic acids, lactic acid, and mandelic acid were used by Brunner [13], but, as mentioned above, these ligands did not afford very enantioselective catalysts. Aminoacids provided the possibility of introducing bulky substituents at the nitrogen atom, but these ligands based on proline and phenylanaline also gave modest results (Figure 17.12). 

Since the pioneering studies of asymmetric catalysis with core-functionalized dendrimers reported by Brunner (88) and Bolm (89), several noteworthy investigations have been described in this field. Some examples of the dendritic effects observed in enantioselective catalysis with dendrimers having active sites in the core were discussed in Section II, such as the catalytic experiments with TADDOL-cored dendrimers described by Seebach et al. (59) the asymmetric addition of Et2Zn to aldehydes catalyzed by core-functionalized phenylacetylene-containing dendrimers reported by Hu et al (42)-, the asymmetric hydrogenation investigations with (R)-BINAP core-functionalized dendrimers synthesized by Fan et al. (36) or the results... 

With modified Aratani catalysts (2, R = Ph and A = CH2Ph), Reissig observed moderate enantioselectivities (30-40% ee for the trans cyclopropane isomer) for reactions between trimethylsilyl vinyl ethers and methyl diazoacetate [26], but vinyl ethers are the most reactive olefins towards cyclopropanation and also the least selective [30,31]. Other chiral Schiff bases have been examined for enantio-selection by using the in situ method for catalyst preparation that was pioneered by Brunner, but enantioselectivities were generally low [32]. 

Brunner et al. reported core-functionalised dendrimer metal catalysts ("dendri-zyme ) for use in enantioselective catalysis [lb, 10, 11]. Optically active dendrimer ligands were used, for example for the reaction of styrene with ethyl diazoacetate in a Cu(I)-catalysed enantioselective cyclopropanation. The starting compound for the preparation of these ligands was L-aspartic acid. However, (IS,2 S)-2-amino-1-phenyl-1,3-propanol can also serve as reactant for the synthesis of optically active dendrimer ligands. 

Brunner, H., (1995) Dendrizymes Expanded ligands for enantioselective catalysis J. Organomet. Chem. 500, 39-46. 

H. Brunner, W. Zettlmeier, Handbook of Enantioselective Catalysis with Transition Metal Compounds, Vol. II, VCH, Weinheim, 1993 J. Holz, M. Quirmbach, A. Borner, Synthesis 1997, 983-1006 M. Ohff, J. Holz, M. Quirmbach, A. Borner, Synthesis 1998, 1391-1415. 

Reetz MT, Brunner B, Schneider T, Schulz F, Clouthier CM, Kayser MM (2004a) Directed evolution as a method to create enantioselective cyclohexanone monooxygenases for catalysis in Baeyer-Villiger reactions. Angew Chem Int Ed 43 4075 1078... 

For a review on enantioselective catalysis with transition metal compounds, see H. Brunner, Quim. Nova, 1995,18, 603. 

For reviews see (a) Ojima I (ed) (1993) In Catalytic asymmetric synthesis. VCH, New York (b) Noyori R (1994) In Asymmetric catalysis in organic synthesis. WUey, New York (c) Brunner H, Zettimeier W (1993) In Handbook of enantioselective catalysis with transition metal compounds. VCH, Weinheim (d) Jacobsen EN, Pfaltz A, Yamamoto H (eds) (1999) In Comprehensive asymmetric catalysis. Springer, Berlin Heidelberg New York... 

Brunner and Miiller (84). Various drugs have been found to bind enantio-selectively to AGP. The laevorotatory enantiomer of propranolol (Fig. 3B) is preferentially bound to AGP (42,85), the ratio of the free fractions (- +) being 0.79. This enantioselectivity is apparent over a range of AGP concentrations (85,86). Interestingly, the enantioselectivity in binding of propranolol to HSA is inverted, compared to that of AGP (42). The significant difference in the tissue distribution of the enantiomers of... 

H. Brunner, W. Zettlmeier, Handbook of Enantioselective Catalysis, VCH, Weinheim, 1993. 

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