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PubMed2006

Lithium diisopropylamide-mediated ortholithiation and anionic fries rearrangement of aryl carbamates: role of aggregates and mixed aggregates.

Structural and mechanistic studies of the lithium diisopropylamide (LDA)-mediated anionic Fries rearrangements of aryl carbamates are described. Substituents at the meta position of the arene (H, OMe, F) and the dialkylamino moiety of the carbamate (Me(2)N, Et(2)N, and i-Pr(2)N) markedly influence the relative rates of ortholithiation and subsequent Fries rearrangement. Structural studies using (6)Li and (15)N NMR spectroscopies on samples derived from [(6)Li,(15)N]LDA reveal an LDA dimer, LDA dimer-arene complexes, an aryllithium monomer, LDA-aryllithium mixed dimers, an LDA-lithium phenolate mixed dimer, and homoaggregated lithium phenolates. The highly insoluble phenolate was characterized as a dimer by X-ray crystallography. Rate studies show monomer- and dimer-based ortholithiations as well as monomer- and mixed dimer-based Fries rearrangements. Density functional theory computational studies probe experimentally elusive structural and mechanistic details.

Anions↗
PubMed1976

Synthesis and biological activities of 5-trifluoromethyl-5'-azido-2',5'-dideoxyuridine and 5-trifluoromethyl-5'-amino-2',5'-dideoxyuridine.

5-Trifluoromethyl-2'-deoxyuridine (1) was tosylated with p-toluenesulfonyl chloride in dry pyridine at 3 degrees to give 5-trifluoromethyl-5'-O-(p-tolylsulfonyl)-2'-deoxyuridine (2), which was converted to 5-trifluoromethyl-5'-azido-2',5'-dideoxyuridine (3) by reacting with lithium azide in N,N-dimethylformamide at 85-90 degrees for 2 h. Compound 3 was then hydrogenated in ethanol-water (1:1, v/v) at room temperature and 35 psi of hydrogen pressure, using 10% palladium on charcoal as cstalyst, to yield 5-trifluoromethyl-5'-amino-2',5'-dideoxyuridine (4). Compound 4 is about fourfold less potent than compound 1 as an antiviral agent but is about 40-fold less toxic to the host Vero cells. Thus the therapeutic index of compound 1 has been improved by a factor of 10 by replacement of the 5'-hydroxyl with an amino group. Compound 1, however, is more than 100-fold more inhibitory to Sarcoma 180 cells in culture relative to compound 4. Compound 3 is markedly less potent than compound 1 or 4 as either an antiviral or an antineoplastic compound.

Animals↗
PubMed2001

The synthesis of homoallylic amines utilizing a cuprate-based 1,2-metalate rearrangement.

Lithiation of the N-2,4,6-triisopropylbenzenesulfonyl-2-pyrroline (16) and treatment of the resulting cyclic vinyllithium reagent with R2CuCNLi2 produced an acyclic vinyl organometallic species that, when treated with an electrophile (H2O or RX), gave the homoallylic sulfonamides 18a-k in 37-93% yields and in > 95% diastereoselectivity. The deprotection of a representative homoallylic sulfonamide 18d was achieved in 83% yield by sonication in the presence of lithium wire and catalytic 4,4'-di-tert-butylbiphenyl (DBB). The efficacy of this general procedure for the production of homoallylic amine derivatives is demonstrated by the preparation of the diene amine 25, a key intermediate in the synthesis of a squalene synthetase inhibitor.

Amines↗
PubMed2004

Total synthesis of the proposed structures of indole alkaloids lyaline and lyadine.

The harman-1,4-dihydropyridines 1 and 2, which constitute the originally proposed structures for the indole alkaloids lyaline and lyadine, have been synthesized, and their NMR data have been compared with those available for the natural products. Due to the discrepancies in the spectral data, the structures of lyadine and lyaline should be revised.

Indole Alkaloids↗
PubMed2004

Improved synthesis of aryltrialkoxysilanes via treatment of aryl Grignard or lithium reagents with tetraalkyl orthosilicates.

General reaction conditions for the synthesis of aryl(trialkoxy)silanes from aryl Grignard and lithium reagents and tetraalkyl orthosilicates (Si(OR)(4)) have been developed. Ortho-, meta-, and para-substituted bromoarenes underwent efficient metalation and silylation at low temperature to provide aryl siloxanes. Mixed results were obtained with heteroaromatic substrates: 3-bromothiophene, 3-bromo-4-methoxypyridine, 5-bromoindole, and N-methyl-5-bromoindole underwent silylation in good yield, whereas a low yield of siloxane was obtained from 2-bromofuran, and 2-bromopyridine failed to give silylated product. The synthesis of siloxanes via organolithium and magnesium reagents was limited by the formation of di- and triarylated silanes (Ar(2)Si(OR)(2) and Ar(3)SiOR, respectively) and dehalogenated (Ar-H) byproducts. Silylation at low temperature gave predominantly monoaryl siloxanes, without requiring a large excess of the electrophile. Optimal reaction conditions for the synthesis of siloxanes from aryl Grignard reagents entailed addition of arylmagnesium reagents to 3 equiv of tetraethyl- or tetramethyl orthosilicate at -30 degrees C in THF. Aryllithium species were silylated using 1.5 equiv of tetraethyl- or tetramethyl orthosilicate at -78 degrees C in ether.

Catalysis↗
PubMed2004

Ion pair first and second acidities of some beta-diketones and aggregation of their lithium and cesium enediolates in THF.

Ion pair pK values were measured for three beta-diketones in THF, 1-3, with lithium and cesium counterions. The results showed variations with concentration indicative of aggregation of the metal enolates to dimers. Similarly, ion pair pK values could be determined for some of these metal enolates going to the corresponding dimetal dienediolates which were also found to form dimers. These equilibria are more complicated to analyze because aggregation affects both sides of the proton transfer equilibria. The results show that all of the species measured exist mostly as dimers at concentrations >0.01 M typical of most organic synthesis reactions and physical measurements. NMR measurements show that the enols of 1 and 2, which can undergo intramolecular hydrogen bonding, predominate in both THF and DMSO solutions, whereas 3, whose enols cannot be so stabilized, is mostly keto in THF but approximately equimolar enol and keto in DMSO. Dimerization of the monolithium salts is rapid on the NMR time scale but that of the dilithium salts is slow.

Anions↗
PubMed2006

A facile one-pot preparation of alkyl aminoaryl sulfides for the synthesis of GW7647 as an agonist of peroxisome proliferator-activated receptor alpha.

We have developed two simple and high yielding one-pot syntheses of alkyl aminoaryl sulfides containing a series of four-steps: in situ protection of the free amine by reaction with a Grignard reagent, halogen-lithium exchange, sulfur insertion, and a substitution reaction with various electrophiles. Through this protocol, we have successfully synthesized tert-butyl-2-[4-(2-aminoethyl)phenylsulfanyl]-2-methylpropanoate, a key intermediate for the synthesis of GW7647 and GW9578 (ureido-TiBAs), in 92% yield. Furthermore, we were able to improve the overall yield of GW7647 to 66%, 3 times the yield previously reported.

Amines↗
PubMed2006

Experimental and theoretical studies on radical trifluoromethylation of titanium ate and lithium enolates.

The radical trifluoromethylation of Ti ate and Li enolates has been investigated by both experiments and density functional (UB3LYP/6-311+G//UB3LYP/6-31+G*) calculations. Radical CF3 addition to the enolates proceeds in a highly exothermic manner without significant reaction barriers in both Ti ate and Li enolates. There are two possible reaction paths after the addition of CF3 radical in the case of Ti ate enolate; one is the elimination of Ti(III) from the ketyl radical intermediate and the other is the direct reaction of the ketyl radical intermediate with CF3I. However, in the case of Li enolate, only the latter path is possible due to the high energy barrier of the elimination of the Li radical. This analysis provides an explanation of the experimental observation that the Li enolate could form the radical cycle efficiently but the Ti ate enolate could not. To make the radical cycle complete, I- has to be extracted from CF3I itself or the radical anion of CF3I. In the case of Li, formation of Li-I bond could be the driving force for the extraction of I- and regeneration of CF3 radical. However, Ti does not give exothermic Ti-I formation and thus regeneration of CF3 radical is less likely.

Free Radicals↗
PubMed2006

Elucidation of the redox behavior of 2,5-dimercapto-1,3,4-thiadiazole (DMcT) at poly(3,4-ethylenedioxythiophene) (PEDOT)-modified electrodes and application of the DMcT-PEDOT composite cathodes to lithium/lithium ion batteries.

The redox reactions of DMcT at PEDOT-modified glassy carbon electrodes (GCEs) in acetonitrile (AN) have been investigated via cyclic voltammetry (CV) and the electrochemical quartz crystal microbalance (EQCM) in order to elucidate the redox reaction mechanism. A redox couple at -0.29 V versus Ag/Ag+ was assigned to the dimerization process of singly protonated DMcT (DMcT-1H), and a second couple observed at +0.42 V was assigned to the polymerization process of the protonated DMcT dimer. Our investigations revealed further that the anodic current response at +0.55 V (polymerization process) has a shoulder at +0.38 V ascribed to the dimerization process of doubly protonated DMcT (DMcT-2H), indicating that the redox couple at +0.42 V is the overlapping response of the polymerization of the protonated DMcT dimer and the dimerization of the DMcT-2H monomer. It was also confirmed that the dimerization process of DMcT-1H at -0.29 V proceeded not only at the surface of a PEDOT film but also inside the film as previously suggested. Moreover, the thermodynamics of these redox reactions at PEDOT-modified GCEs are dependent on the basicity (or acidity) of the solution, as anticipated and previously shown at unmodified GCEs. The oxidation of DMcT occurs at less positive potentials and the reduction occurs at more negative potentials in the presence of base. On the basis of the results obtained, the full redox reaction scheme for DMcT at a PEDOT-modified GCE is proposed.

Anions↗
PubMed2001

A new polymer-anchored chiral catalyst for asymmetric Michael addition reactions.

[figure: see text] Monomer (R,R)-3-aza-3-(p-vinylbenzyl)-1,5-diphenyl-1,5-dihydroxypentane (2) when polymerized with styrene and divinylbenzene affords polymers, onto which lithium and aluminum are incorporated via reaction with lithium aluminum hydride. The resulting insoluble polymers containing chiral lithium and aluminum active centers are quite effective for asymmetric Michael addition of nitro compounds, thiols, and amines. The optimized reaction conditions yield Michael adducts in good yield with high enantiomeric excesses.

Journal Article↗
PubMed2003

Development of novel diastereoselective alkenylation of enolates using alkenylselenonium salts.

[reaction: see text] A novel alkenylation of enolates using alkenylselenonium salts is described. A reaction of lithium enolates, which were prepared in situ by the reaction of LiHMDS and carbonyl compounds, with alkenylselenonium salts gave the ethenylation products of carbonyl compounds in high yield. Diastereoselective alkenylation was also accomplished by the reaction of the enolates derived from N-acyl-1,3-oxazolidin-2-ones with the alkenylselenonium salt to afford good results (up to 92% yield and up to 95% de).

Journal Article↗
PubMed2005

No-D NMR study of the pathway for n-BuLi "oxidation" of 1,5-cyclooctadiene to dilithium cyclooctatetraene dianion [Li2COT2-].

[Reaction: see text] The transformation of 1,5-cyclooctadiene (1) into cyclooctatetraene (3) by way of dianion 2 is an interesting reaction of considerable preparative value. The mechanism was initially suggested to involve lithium hydride loss from 4a/4b, followed by two deprotonations to produce 2. This No-D 1H NMR study indicates the long-term stability of 4a/4b (in the absence of additional n-BuLi) and suggests a different mechanistic sequence, in which 4a/4b is deprotonated a second time prior to LiH ejection.

Alkadienes↗
PubMed2006

Enantioselective synthesis of functionalized medium-sized oxacycles.

Enantioselective routes to functionalized, seven-, eight-, and nine-membered oxacycles that are amenable to further elaboration have been developed. Salient features of the methodology include highly diastereoselective and regioselective transformations of an ephedrine-derived epoxy morpholinone to functionalized precursors of the oxacycles. The ephedrine scaffold exerts remote stereocontrol in the functionalization of the appended oxacycle. [reaction: see text]

Cyclization↗
PubMed1999

Unusual conformational effect in alpha-aminoorganostannanes.

[formula: see text] Dynamic NMR analysis of conformationally mobile and rigid 2-tributylstannyl-N-methylpiperidines revealed an unexpected conformational effect that is manifested in a small energy difference between conformers in which the tin is equatorial and axial. The major reason appears to be a distortion of the conformer in which the C-2-Sn bond is synclinal to the nitrogen lone pair.

Lithium↗
PubMed1972

Potassium ion-stimulated and sodium ion-dependent adenosine diphosphate-adenosine triphosphate exchange activity in a kidney microsomal fraction.

1. K(+) did not affect the Mg(2+)-dependent transphosphorylation but markedly increased the Na(+)-stimulated ADP-ATP exchange rate mediated by a microsomal fraction from guinea-pig kidney. 2. Rb(+), Cs(+), NH(4) (+) and Li(+) were equally effective in stimulating the Na(+)-dependent ADP-ATP exchange activity. 3. Treatment of the microsomal fraction with N-ethylmaleimide or increased concentrations of Mg(2+) prevented stimulation of the Na(+)-dependent exchange reaction by K(+). 4. Ouabain (2.5mum) inhibited ATP hydrolysis by 33% but did not decrease the K(+)-stimulated Na(+)-dependent ADP-ATP exchange rate. 5. A possible mechanism for stimulation of exchange activity by K(+) is discussed.

Adenosine Diphosphate↗