Solvents sparteine

Solvent extraction techniques are useful in the quantitative analysis of niobium. The fluoro complexes are amenable to extraction by a wide variety of ketones. Some of the water-insoluble complexes with organic precipitants are extractable by organic solvents and colorimetry is performed on the extract. An example is the extraction of the niobium—oxine complex with chloroform (41). The extraction of the niobium—pyrocatechol violet complex with tridodecylethylammonium bromide and the extraction of niobium—pyrocatechol—sparteine complex with chloroform are examples of extractions of water-soluble complexes. Colorimetry is performed on the extract (42,43). Colorimetry may also be performed directly on the water-soluble complex, eg, using ascorbic acid and 5-nitrosahcyhc acid (44,45). 

The first studies leading to the deracemization of VANOL 93 and VAPOL 94 were carried out with 1.4 equiv. of copper chloride and 2.8 equiv. of (-)-sparteine 1 in a mixture of methanol and methylene chloride (1 3.4) de-oxygenated by an argon purge, which gave a 64% yield of (S)-VAPOL with 99% ee, and a 77% yield of (S)-VANOL with 99% ee. However, in the last case, the co-solvent was deoxygenated via a freeze-thaw method. 

Sigman et al. have optimized their system too [45]. A study of different solvents showed that the best solvent was f-BuOH instead of 1,2-dichloroethane, which increased the conversion and the ee. To ensure that the best conditions were selected, several other reaction variables were evaluated. Reducing the catalyst loading to 2.5 mol % led to a slower conversion, and varying temperature from 50 °C to 70 °C had little effect on the selectivity factor s. Overall, the optimal conditions for this oxidative kinetic resolution were 5 mol % of Pd[(-)-sparteine]Cl2, 20 mol % of (-)-sparteine, 0.25 M alcohol in f-BuOH, molecular sieves (3 A) at 65 °C under a balloon pressure of O2. 

Methods for the enantioselective synthesis of 3-substituted indolines by means of the asymmetric intramolecular carbolithiation of 2-bromo-A,-allylanilines in the presence of (-)-sparteine were reported simultaneously by Bailey <00JA6787> and Groth <00JA6789>. Thus, addition of 89 to 2.2 equiv of /BuLi in the presence of the chiral ligand generates the lithium intermediate 90 which upon quenching with methanol affords the chiral indoline 91 in a process that is highly solvent dependent. 

In 1996, Burgess et al. (34) reported one of the first examples of a formal attempt to use a parallel approach in the optimization of a catalytic reaction. Previously, Sulikowski reported the copper catalyzed C-H insertion of a diazoester. In an attempt to optimize the selectivity for this reaction, three different bis(oxa-zoline) ligands, a bis(salicylidine)ethylenediamine(salen)-type ligand and sparteine were screened in combination with seven different metals and four different solvents (Scheme 13). Ligand 116 in tetrahydrofuran (THF) solvent at slightly reduced temperature proved to be the best reaction conditions, giving a 3.9 1 product ratio and good yield. 

The presence of organolithium compounds in etheric solvents at temperatures above 0°C may lead to extensive decomposition of the solvent and solute a slow electron transfer side reaction of lithium naphthalene or sodium naphthalene with the THE solvent (equation 5) has been reported . The three isomeric forms of BuLi were shown to induce extensive decomposition of THE. The main path for this process is metallation at position 2 of THE, leading to ring opening and elimination of ethylene. An alternative path is proton abstraction at position 3, followed by ring opening. The presence of additives such as (—)-sparteine (24), DMPU (25), TMEDA and especially HMPA does not prevent decomposition but strongly affects the reaction path. ... 

Another inconvenience of polyaldehyde resists was the softness of the films. The copolymer of 4,4,4-triphenylbutanal and butanal prepared using a C2H5MgBr-(-)-sparteine complex (24) dissolves easily in certain organic solvents and forms a fairly hard resist film. The copolymer containing 8 mol% of the former monomer units showed a sensitivity of 1.7 x 10-6 C/cm2 (25). 

In spite of the difficulty in definitely characterizing alkaloids by definition, they do have a surprising number of physical and chemical properties in common. For the most part, the alkaloids are insoluble or sparingly so in water but form salts (by metathesis or addition) that are usually freely soluble. The free alkaloids are usually soluble in ether or chloroform, or other immiscible solvents, in which, however, the alkaloidal salts are insoluble. This permits the isolation and purification of the alkaloids as well as their quantitative estimation. Most of the alkaloids are crystalline solids, although a few are either amorphous (coniine, nicotine, sparteine) or liquid. It is interesting to note that the liquid alkaloids have no oxygen in their molecules. Alkaloidal salts are invariably crystalline, and their crystal form and habit are often useful in their rapid microscopical identification (Sollmann, 1944). 

The effects of different solvents and palladium catalyst ligands on the allylic alkylation of aryl a-cyano esters have been investigated 133 up to 55% ee has been obtained in the presence of (-)-sparteine in THF at room temperature. 

A similar effect controls the lithiation and substitution of the benzylic carbamate 86.33 35 Lithiation of 86 with s-BuLi-(-)-sparteine in ether gives low enantiomeric excesses, but when the lithiation is carried out in hexane, a solvent in which the intermediate complex is not soluble, the enantiomeric excess of the product 88 increases to 82%. Even higher enantiomeric excesses are obtained if the intermediate suspension of organolithium-(-)-... 

Sparteine is recovered by making the aqueous phases basic with aqueous 20% sodium hydroxide (NaOH) (160 mL) (Note 14). The aqueous phase is extracted with EtgO (4 x 150 mL), and the combined organic phases are dried over potassium carbonate (K2C03), filtered, and the solvents removed under reduced pressure to afford 30.3 g (98%) of crude, recovered sparteine as a pale yellow oil (Note 15). Fractional distillation of the residual oil from calcium hydride (CaH2) (Note 5) affords 27.0 g of sparteine (88%) suitable for reuse. 

Sparteine is liberated from the commercially available sulfate salt (Aldrich Chemical Company, Inc.) as follows Sparteine sulfate pentahydrate (100 g, 240 mmol) is dissolved in deionized water (125 mL), and to this solution is slowly added aqueous 20% NaOH (100 mL). The resulting milky-white, oily mixture is then extracted with ether (4 x 150 mL). The combined ethereal extracts are dried over anhydrous K2CO3, filtered, and the solvent is removed under reduced pressure. Vacuum distillation of the residual oil from CaH2 affords 52 g (92%) of sparteine as a clear, colorless to slightly yellow, viscous oil (bp 115-120°C/0.3 mm). The sparteine free base readily absorbs atmospheric carbon dioxide (CO2) and should be stored under argon at -20°C in a freezer. 

A Pd-catalyzed oxidative cyclization of phenols with oxygen as stoichiometric oxidant in the noncoordinating solvent toluene has been developed for the synthesis of dihydrobenzo[ ]furans (Equation 136). Asymmetric variants of this Wacker-type cyclization have been reported by Hayashi and co-workers employing cationic palladium/2,2 -bis(oxazolin-2-yl)-l,l -binaphthyl (boxax) complexes <1998JOC5071>. Stoltz and co-workers have reported ee s of up to 90% when (—)-sparteine is used as a chiral base instead of pyridine <2003AGE2892, 2005JA17778>. Attempts to effect such a heteroatom cyclization with primary alcohols as substrates, on the other hand, led to product mixtures contaminated with aldehydes and alkene isomers, which is in contrast to the reactions with the Pd(ii)/02 system in DMSO <1995TL7749>. 

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