Optically active pyridine derivatives 2, 15, 18, 19, 21, 26, and 27 are obtained by enantioselective reduction of the corresponding ketones 5, 7, 11–13, 24, and 25 using the chiral borane reagent chlorodiisopinocampheylborane [(Ipc)2BCl]. Nickel(0)‐mediated coupling of bromopyridines 2, 15, and 31 gives C2‐symmetric 2,2′‐bipyridines (R,R)‐32, (R,R′)‐33, and (S,S)‐38, respectively, which form metal complexes with CoII, PdII, CuI, and AgI. Aryl‐substituted pyridines 26, and 39–41 are synthesized by palladium(0)‐catalyzed cross couplings of 2 and 15 with boronic acids 42–44.

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Conjugate addition of diethylzinc to enones is catalyzed by a complex derived from Ni(acac)2 and C2-symmetric 2,2'-bipyridine 3 or chiral pyridines 5-12. The products are obtained with optical purities up to 89% ee. A strong positive nonlinear relationship between the enantiomeric excess of the ligand and the ee of the product has been observed. The factors which govern catalyst activity and enantioselectivity have been investigated.Carbon -carbon bond formation by conjugate addition of organometallic reagents to a$-unsaturated enones is an efficient and reliable method for the synthesis of P-substituted carbonyl compounds. In particular, organocopper reagents have successfully been applied to regio-, chemo-and stereoselective alkylations['l. Enanlioselectiue conjugate additions of organometallics were first described by Kretschmer['"I and Seebach[2bsc1 using sparteine or 1,4-(dialkylamino)-2,3-dimethoxybutane, respectively, as chiral coordinating ligands. Leyendecker['dl employed N-alkylprolinol, and recently Alexakis[''] used chiral phosphorus derivatives to induce asymmetry during the conjugate addition. Other efforts have focused on the development of organo(heter0)cuprates carrying optically active nontransferable ligands13]. In some cases, enantioselectivities up to 97% were achieved. In general, these methods require stoichiometric or often excess amounts of chiral reagents. Despite the increasing importance of catalytic enantioselective transformations, reports on chiral catalysts for conjugate addition reactions are still rarec4]. Lippard et al. reported that copper(1) complexes with bidentate N,N-dialkyl-substituted aminotropone imines catalyze the 1,4-addition of n-butylmagnesium chloride to ~yclohexenone[~1. The corresponding product was obtained with up to 74% ee. However, the scope of this reaction is rather limited, and other reactants gave products with very low enantiomeric excess. Jansen and Feringa described the conjugate addition of Grignard reagents to enones catalyzed by chiral zinc(I1) complexes derived from diamines and amino alcohols[61. With this system, optical yields up to 33% ee were achieved. Based on some earlier work by Luche et al.I7], Soai and co-workers developed an enantioselective modification of the nickel-catalyzed alkyl transfer from diorganozincs to enones [']. A complex prepared in situ from nickel acetylacetonate [Ni(acac),] and N,N-dialkylnorephedrine afforded the products with moderate to good enantioselectivity. The degree of asymmetric induction could then be substantially raised by the addition of achiral ligands such as 2,2'-bipyridine or 1, lOphenanthroline[8a1. Our interest in this area derived from our previous work on the enantioselective alkylation of aldehydes catalyzed by optically active bipyridines and pyridine derivative^ [^^'^]. We found that nickel complexes of C2-symmetric bipyridine 3["] catalyzed the conjugate addition of diethylzinc to chalcones and afforded addition products with high enantiomeric excess[121. In this paper, we describe further d...

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Manipulation von Mikropartikeln: Die Photoisomerisierung von grenzflächenaktiven Substanzen, die an einer Gas‐Flüssigkeits‐Grenzfläche adsorbiert sind, treibt einen Marangoni‐Fluss an, in dem kleine Partikel gefangen und manipuliert werden können. Durch Umschalten der Laserwellenlänge kann ein Fluss erzeugt werden, der entweder hin zum oder weg vom Fokus führt. Das Bild zeigt ein im Zufluss gefangenes Partikel in der Fokalregion.