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Cinchona quinuclidine

It has already been shown that both the laevorotatory and dextrorotatory cinchona alkaloids on degradation yield scission products from the quinuclidine nucleus, which are structurally and optically identical, for example, meroquinenine, [a] -f- 27 6° d-/3-cincholoiponic acid. [Pg.443]

These changes have been experimentally demonstrated only for quinine and quinidine, but in view of the optical identity of the quinuclidine degradation products from the principal cinchona alkaloids, it may be assumed that in all of them the total dextrorotatory effect at C and C is made up of a dextrorotatory effect at C exceeding a laevorotatory effect at C. ... [Pg.444]

The cinchona alkaloids on degradation break down into derivatives of (1) quinoline and (2) quinuclidine and the synthesis of any one of them involves the preparation of each of these two halves in a form suitable for combination. [Pg.454]

Work also prepared a series of carbinolamines and polyamines without a quinoline nucleus but, in other respects, conforming in type and range of molecular weight, with quinoline compounds known to possess plasmocidal activity. As none of these were active, it seems clear that the quinoline nucleus in the cinchona alkaloids and in certain synthetic anti-malarials is a potent factor in the production of plasmocidal action. Later the same author made (1942) a series of lepidylamine derivatives of the form R. Q. CHj. NH[CH2] . NEtj, which were found to be inactive, in spite of their similarity to the active examples of the type R. Q. NH[CH2] . NEt2 prepared by Magidson and Rubtzow. Rubtzow (1939) has also shown that an isomeride of dihydroquinine (II) with the quinuclidine nucleus attached via the carbinol group at C in the quinoline nucleus was inactive in an infection of Plasmodium prcecox in finches. [Pg.475]

Pt/Al2C>3-cinchona alkaloid catalyst system is widely used for enantioselective hydrogenation of different prochiral substrates, such as a-ketoesters [1-2], a,p-diketones, etc. [3-5], It has been shown that in the enantioselective hydrogenation of ethyl pyruvate (Etpy) under certain reaction conditions (low cinchonidine concentration, using toluene as a solvent) achiral tertiary amines (ATAs triethylamine, quinuclidine (Q) and DABCO) as additives increase not only the reaction rate, but the enantioselectivity [6], This observation has been explained by a virtual increase of chiral modifier concentration as a result of the shift in cinchonidine monomer - dimer equilibrium by ATAs [7],... [Pg.535]

A third variation on this theme was recently reported by Hodge (48), who alkylated the cinchona alkaloids on the quinuclidine nitrogen using the well-known chloromethylated cross-linked polystyrenes. Optical yields were low (10 to 30%) and no significant conclusions were drawn. [Pg.97]

The first silica-supported CSP with a cinchona alkaloid-derived chromatographic ligand was described by Rosini et al. [20]. The native cinchona alkaloids quinine and quinidine were immobilized via a spacer at the vinyl group of the quinuclidine ring. A number of distinct cinchona alkaloid-based CSPs were subsequently developed by various groups, including derivatives with free C9-hydroxyl group [17,21-27] or esterified C9-hydroxyl [28,29]. All of these CSPs suffered from low enantiose-lectivities, narrow application spectra, and partly limited stability (e.g., acetylated phases). [Pg.3]

The notable mode of stereoselectivity of Cinchona alkaloids is presented by its psendoenantiomeric pairs which can be employed to generate either enantiomer of chiral prodnct. Key moieties that are central to Cinchona alkaloids are the quinuclidine nitrogen and the adjacent C(9)-OH (the N-C(8)-C(9)-OH moiety) (Fig. 2). In psendoentiomeric alkaloids in the natural open conformation, the torsion angle N-C(8)-C(9)-0 are opposite in sign Q and CD are (-), and thereby induce selectivity for one enantiomer, whereas QD and C are (-I-) and afford the other enantiomer [28, 29],... [Pg.148]

The focus of this review is to discuss the role of Cinchona alkaloids as Brpnsted bases in organocatalytic asymmetric reactions. Cinchona alkaloids are Lewis basic when the quinuclidine nitrogen initiates a nucleophilic attack to the substrate in asymmetric reactions such as the Baylis-Hillman (Fig. 3), P-lactone synthesis, asymmetric a-halogenation, alkylations, carbocyanation of ketones, and Diels-Alder reactions 30-39] (Fig. 4). [Pg.148]

Preliminary mechanistic studies show no polymerization of the unsaturated aldehydes under Cinchona alkaloid catalysis, thereby indicating that the chiral tertiary amine catalyst does not act as a nucleophilic promoter, similar to Baylis-Hilhnan type reactions (Scheme 1). Rather, the quinuclidine nitrogen acts in a Brpnsted basic deprotonation-activation of various cychc and acyclic 1,3-dicarbonyl donors. The conjugate addition of the 1,3-dicarbonyl donors to a,(3-unsaturated aldehydes generated substrates with aU-carbon quaternary centers in excellent yields and stereoselectivities (Scheme 2) Utility of these aU-carbon quaternary adducts was demonstrated in the seven-step synthesis of (H-)-tanikolide 14, an antifungal metabolite. [Pg.150]

In the initial screening of various Cinchona alkaloids, the addition of diethyl phosphate 41 to IV-Boc imine 40 in toluene revealed the key role of the free hydroxyl group of the catalyst. Replacing the C(9)-OH group with esters or amides only results in poor selectivity. Quinine (Q) was identified as an ideal catalyst. A mechanistic proposal for the role of quinine is presented. Hydrogen-bonding by the free C(9)-hydroxyl group and quinuclidine base activation of the phosphonate into a nucleophilic phosphite species are key to the reactivity of this transformation (Scheme 9). [Pg.154]

New catalyst design further highlights the utility of the scaffold and functional moieties of the Cinchona alkaloids. his-Cinchona alkaloid derivative 43 was developed by Corey [49] for enantioselective dihydroxylation of olefins with OsO. The catalyst was later employed in the Strecker hydrocyanation of iV-allyl aldimines. The mechanistic logic behind the catalyst for the Strecker reaction presents a chiral ammonium salt of the catalyst 43 (in the presence of a conjugate acid) that would stabilize the aldimine already activated via hydrogen-bonding to the protonated quinuclidine moiety. Nucleophilic attack by cyanide ion to the imine would give an a-amino nitrile product (Scheme 10). [Pg.155]

A cursory examination of the Cinchona catalysts used in O Donnell-type alkylation [90] of methyl (diphenylimino)glycinate (Appendix 7.A) reveals that only minor modifications to the Cinchona scaffold are required for the synthesis of a catalyst the 8-substituent on the quinuclidine core may either be a vinyl group (as in the parent alkaloids, quinine and quinidine) or can be an ethyl substituent, introduced by hydrogenation. The quinoline system at the 2-position ofthe quinuclidine ring can be unsubstituted if the catalyst is derived from quinine or quinidine, but can contain a 6-methoxy group ifit is derived from cinchonine or cinchonidine. The 3-position ofthe quinuclidine ring may contain either a hydroxy group or else a vinyloxy or benzyloxy... [Pg.174]

Certain tertiary amines such as pyridine or a-quinuclidine accelerate the stoichiometric reaction between osmium tetroxide and olefins (86). An asymmetric olefin osmylation using stoichiometric amounts of cinchona alkaloids as the chiral ligands was described in 1980 (87a). Optical yields of up to 90% were attained with frans-stilbene as substrate. [Pg.84]

Cinchona alkaloids, naturally ubiquitous /3-hydroxy tertiary-amines, are characterized by a basic quinuclidine nitrogen surrounded by a highly asymmetric environment (12). Wynberg discovered that such alkaloids effect highly enantioselective hetero-[2 -I- 2] addition of ketene and chloral to produce /3-lactones, as shown in Scheme 4 (13). The reaction occurs catalytically in quantitative yield in toluene at — 50°C. Quinidine and quinine afford the antipodal products by leading, after hydrolysis, to (S)- and (/ )-malic acid, respectively. The presence of a /3-hydroxyl group in the catalyst amines is not crucial. The reaction appears to occur... [Pg.366]

At the moment we have no good explanation for the observed acceleration except that it has a connection to the basic character of the quinuclidine part and the adsorption behavior of the cinchona molecule. In addition, we think that the rate and product determining steps occur on the platinum surface and that well defined interactions between the platinum surface (ensembles), one cinchona molecule and the a-ketoester are crucial. There are, of course, other possible explanations for the observed enantioselection. Wells and Thomas [80] have proposed that an array of... [Pg.89]

Quinuclidine (l-azabicyclo[2.2.2]octane) is a heterocyclic system which is part of the structure of a number of natural physiologically active compounds and synthetic drugs.1 Among the natural alkaloids, the following quinoline and indole derivatives contain the quinuclidine ring cinchonine, cinchonamine (alkaloids of Cinchona species),8-12... [Pg.473]

The following facts can be deduced from Sharpless study a) the ligands have a substantial accelerating effect on the reaction rate b) the bis-cinchona alkaloids are uniformly more effective than the monodentate quinuclidine and c) the increase in rate is substrate-dependent. [Pg.407]

Early work from the McIntosh group [1 lh,85] and extensive research from the Dehmlow group [24e-i,48b] concerning chiral catalyst design is noted. Recently, Lygo and co-workers have reported short enantio- and diastereoselective syntheses of the four stereoisomers of 2-(phenylhydroxymethyl)quinuclidine. The authors report that these compounds, which contain the basic core structure of the cinchona alkaloids, will be examined as possible chiral control elements in a variety of asymmetric transformations [86]. [Pg.732]


See other pages where Cinchona quinuclidine is mentioned: [Pg.455]    [Pg.458]    [Pg.464]    [Pg.465]    [Pg.474]    [Pg.1051]    [Pg.56]    [Pg.56]    [Pg.226]    [Pg.513]    [Pg.4]    [Pg.5]    [Pg.29]    [Pg.147]    [Pg.148]    [Pg.162]    [Pg.272]    [Pg.564]    [Pg.255]    [Pg.256]    [Pg.263]    [Pg.147]    [Pg.87]    [Pg.359]    [Pg.404]    [Pg.49]    [Pg.136]    [Pg.5]    [Pg.10]    [Pg.193]    [Pg.204]    [Pg.214]   


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