Phenanthroline derivative chiral

Ligand 92 was readily prepared by reaction of (+)-pinocarvone with 1-phenacylpyridinium iodide. The authors similarly prepared corresponding 5,6-dihydro-1,10-phenanthrolines derived from (+)-pinocarvone and a tetrahydroquinolone (structure 93, [127]) and obtained up to 81% in the palladium-catalyzed test reaction. Chelucci et al. [ 128] reported the synthesis of chiral Ci-symmetric 1,10-phenanthrolines incorporated in asteroid backbone. Structure 94 derived from 5o -cholestan-4-one in Scheme 51, allowed very high yield and up to 96% ee using BSA and tetrabutylammonium fluoride to generate the malonate anion. 

The amino acid derived chiral oxazolidinone 188 is a very commonly used auxiliary in Diels-Alder and aldol reactions. However, its use in diastereoselective 1,3-dipolar cycloadditions is less widespread. It has, however, been used with nitrile oxides, nitrones, and azomethine ylides. In reactions of 188 (R = Bn, R =Me, R = Me) with nitrile oxides, up to 92% de have been obtained when the reaction was performed in the presence of 1 equiv of MgBr2 (303). In the absence of a metal salt, much lower selectivities were obtained. The same observation was made for reactions of 188 (R = Bn, R = H, R = Me) with cyclic nitrones in an early study by Murahashi et al. (277). In the presence of Znl2, endo/exo selectivity of 89 11 and up to 92% de was observed, whereas in the absence of additives, low selectivities resulted. In more recent studies, it has been shown for 188 (R =/-Pr, R = H, R =Me) that, in the presence of catalytic amounts of Mgl2-phenanthroline (10%) (16) or Yb(OTf)3(20%) (304), the reaction with acyclic nitrones proceeded with high yields and stereoselectivity. Once again, the presence of the metal salt was crucial for the reaction no reaction was observed in their absence. Various derivatives of 188 were used in reactions with an unsubstituted azomethine ylide (305). This reaction proceeded in the absence of metal salts with up to 60% de. The presence of metal salts led to decomposition of the azomethine ylide. 

Chiral catenanes can be obtained by the use of an unsynunetrically substituted 1,10-phenanthroline derivative such as LI 123 in the Cu+-template method. Thus the catenate [Cu(L1124)2] , generated in 12% yield as shown in Scheme 4-26 [247J, is topologically chiral. 

Chiral Phenanthrolines in Asymmetric Catalysis. Synthetic modifications on the Phenanthroline core can provide access to highly valuable chiral phenanthroline derivatives with important applications in asymmetric catalysis (Scheme 1). For example, LI has been utilized in copper-catalyzed allylic oxidations, L2 in palladium-catalyzed allylation reactions, and L3-type ligands in rhodium-catalyzed enantioselective hydrosilylation reactions of acetophenone. ... 

Pyridine-based N-containing ligands have been tested in order to extend the scope of the copper-catalyzed cyclopropanation reaction of olefins. Chelucci et al. [33] have carefully examined and reviewed [34] the efficiency of a number of chiral pyridine derivatives as bidentate Hgands (mainly 2,2 -bipyridines, 2,2 6, 2 -terpyridines, phenanthrolines and aminopyridine) in the copper-catalyzed cyclopropanation of styrene by ethyl diazoacetate. The corresponding copper complexes proved to be only moderately active and enantios-elective (ee up to 32% for a C2-symmetric bipyridine). The same authors prepared other chiral ligands with nitrogen donors such as 2,2 -bipyridines 21, 5,6-dihydro-1,10-phenanthrolines 22, and 1,10-phenanthrolines 23 (see Scheme 14) [35]. 

Helquist et al. [129] have reported molecular mechanics calculations to predict the suitability of a number of chiral-substituted phenanthrolines and their corresponding palladium-complexes for use in asymmetric nucleophilic substitutions of allylic acetates. Good correlation was obtained with experimental results, the highest levels of asymmetric induction being predicted and obtained with a readily available 2-(2-bornyl)-phenanthroline ligand (90 in Scheme 50). Kocovsky et al. [130] prepared a series of chiral bipyridines, also derived from monoterpene (namely pinocarvone or myrtenal). They synthesized and characterized corresponding Mo complexes, which were found to be moderately enantioselective in allylic substitution (up to 22%). 

Among several dipyridine derivatives developed as chiral ligands, a Rh catalyst with phenanthroline 13b having a pinane skeleton gave 4 with 76% ee in the reduction of 1, which was higher than that obtained with Rh-phenanthroline-oxazoline 13a [20], whereas the tetraden-tate dipyridine-bis(oxazoline) Bipymox 14 in combination with RhCl, gave 4 with 90% ee (S) [21]. 

Some noteworthy reviews on applications of pyridines and their derivatives deal with oligopyridine liquid crystals as novel building blocks for supramolecular architectures based on metal coordination and hydrogen bonding <2000AGE2454>, enantioselective automultiplication of chiral pyridylalkanols by asymmetric autocatalysis <2000ACR382>, and photoactive mono- and polynuclear Cu(i)-phenanthrolines <2001CSR113>. 

There are several excellent photosensitizers one of them is [Ru(bpy)3]2+ [6]. There are two optical isomers in this complex one is A [Ru(bpy)3]2+ and the other is A-[Ru(bpy)3]2 +, as shown in Scheme 1. Thus one can expect to perform the stereoselective electron transfer reaction with A- and A-[Ru(bpy)3]2 +. Unfortunately, however, the racemization of [Ru(bpy)3]2+ is induced photochemically [7]. The reasonable way to suppress the photoracemiza-tion of this complex is to introduce the optically active organic functional group into the transition metal complexes, as will be discussed in Sec. II.B. The other photosensitizer that is useful for the photoinduced electron transfer reaction is the copper(I) complexes with 1,10-phenanthroline and their derivatives [8,9]. Zinc(II) porphyrin is also an excellent photosensitizer for photoinduced electron transfer reaction [10]. In these complexes, molecular chirality does not exist, unlike in [Ru(bpy)3]2 +. Thus one must introduce some chiral functional group into these compounds, to use these complexes as chiral photosensitizers. 

Thus one can expect that the copper complexes with 2,2 -bipyridine, 1,10-phenanthroline, and their derivatives are successfully applied to asymmetric photoreactions, as with chiral ruthenium(II) complexes, if the optically active moiety is introduced to the ligand, as discussed above (see introduction). 

Since the copper complexes, [Cu(NN)2]+ and [Cu(NN)(PR3)2]+ (NN = 1,10-phenanthroline, 2,2 -bipyridine, and their derivatives) were applied to stoichiometric and catalytic photoreduction of cobalt(III) complexes [8a,b,e,9a,d], one can expect to perform the asymmetric photoreduction system with the similar copper(l) complexes if the optically active center is introduced into the copper(I) complex. To construct such an asymmetric photoreaction system, we need chiral copper(I) complex. Copper complex, however, takes a four-coordinate structure. This means that the molecular asymmetry around the metal center cannot exist in the copper complex, unlike in six-coordinate octahedral ruthenium(II) complexes. Thus we need to synthesize some chiral ligand in the copper complexes. 

Phenanthroline ligands as chiral derivatives for asymmetric catalysis 03EJO1145. 

Chelucci and Thummel reported chiral phenanthrolines containing camphor derivatives 327. Camphor 326, a hindered ketone, causes the Friedlander reaction to proceed in low pelds. They suggested a modification starting from 225 in which 327 forms in 51 % overall 5deld (Scheme 67) (99SC1665). 

The calix[6]arene 65 bridged by a 1,10-phenanthroline was synthesized from p-bu -calix[6]arene and 2,9-bis(bromomethyl)-l,10-phenan-throline (97TL4539). Its complex with Cu has been beneficially used for Cu catalyzed cyclopropanation of styrene and indene. Several chiral derivatives of 65 have been synthesized but the stereoselectivity of cyclopropanation, catalyzed with their Cu complexes, could not be enhanced (2006EJ04717). A similar bridging of calix[5]arene and calix[8]arene has also been investigated (2005EJ02330). 

Fig. 3 (a) The 0(A (left) atropisomer and fran -a -atropisomer (right) with bound isoquinoline in the picket-fence porphyiin receptor (Ref. [29]). (b) The strapped porphyrin receptor with a rigid phenanthroline strap (Ref. [30],). (o) Chiral basket-handle receptor exhibiting a high degree of chiral recognition of amino acid derivatives (Ref [31]). 

More recently, 13,14-dimethyldibenzo[6j][4,7]phenanthroline (55) was synthesized by the copper-catalyzed condensation reactions between 1,4-diiodobenzene (52) and 2-aminoacetophenone (53) to give 54 followed by sulfuric acid-promoted cyclization reactions (Scheme 10) [56]. Alternatively, 55 was also prepared by a one-pot procedure involving the ZnCl2-catalyzed reactions between AA -diphenyl-p-phenylenediamine (56) and acetic acid (Scheme 11) [57, 58]. The enantiomers of 55 were separated by a chiral HPLC column and were found to undergo rapid racemization at room temperature. A slower rate of racemization was observed for the 13,14-diethyl derivative 57. The X-ray structure of 57 confirmed the twisted aromatic framework. 

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