Tetraethylammonium derivatives

The Ugi reaction has been successfully applied to the synthesis of oligopeptide derivatives, c.g.. in the construction of a pure tetra-L-valine derivative69. The 2-methylpropanaldimine 2 of (/7)-l-ferroccnyl-2-rnethylpropylarnine with /V-formyl-L-2-amino-3-methylbulanoic acid (3) as the carboxylic acid component and methyl A/-[(.S)-2-isocyano-3-mcthyl-l -nxo-buLyl -L-2-aiuino-3-inethylbutanoate (4) furnishes the diastereomeric valyl-valyl-valyl-valine derivatives in a ratio (S,S[R],S,S)i(S,R[R],S,S) of 91 9. The stereoselectivity of the process can be enhanced to 98.5 1.5 when two equivalents of tetraethylammonium A -formylvalinate are added. 

TABLE 1 Tetra-alkylammonium Ion, R4N, Transferred from W to DCE by the Coupling with the Redox Reaction Between NADH in W and a Quinone Derivative in DCE. Results After Shaking W Containing 10 M NADH and 10 M (R4N )2 SO4 with DCE Containing 10 M Quinone [Q Chloranil (CQ) or Toluquinone (TQ)] for 1 h. TPenA, TBA, and TEA Denote Tetrapentylammonium, Tetrabutylammonium, and Tetraethylammonium ions. Respectively... 

With certain exceptions, primary fluorination of carbohydrate derivatives is very facile. Fluoride displacement of sulfonyloxy groups by potassium, or cesium, fluoride in 1,2-ethanediol and a variety of other solvents has frequently been used. Tetrabutylammonium (sometimes tetraethylammonium) fluoride in dipolar, aprotic solvents (mainly ace-... 

Armstrong, C.M. (1971) Interaction of tetraethylammonium ion derivatives with the potassium channels of giant axons. The Journal of General Physiology, 58, 413-437. 

Electrolysis of b-al Ionic ketone 61 at a controlled cathode potential of-2.43 V (versus Ag/AgI) in anhydrous DMF using tetraethylammonium p-toluenesulfonate as co-electrolyte provides the derived ketyl radical that undergoes a 5-exo-trig selective ring closure, presumably via transition structure 62 (Scheme 11.19). The cyclization product is further reduced and subsequently protonated to afford traus-configurcd cyclopentanol 63 as single diastereomer in a total yield of 55% [80]. 

Dichloroanthaquinones have also been converted into the corresponding dicyano derivative, via what has been claimed to be the disulphonic acid (vide supra) [76]. Chloropurines have been converted into the corresponding cyano compounds using tetraethylammonium cyanide [77]. 

TEA chloride See tetraethylammonium chloride., te,e a klorjd ) technetium chem A transition element, symbol Tc, atomic number 43 derived from uranium and plutonium fission products chemically similar to rhenium and manganese isotope Tc has a half-life of 200,000 years used to absorb slow neutrons in reactor technology. tek ne-she-om ... 

Vasella has applied the concept of anomeric anion stabilization by a nitro group to the /3-D-JV-acetyl-D-glucosamine derivative 177, available in four steps from N-acetyl-n-glucosamine [52] (Scheme 39). Reaction of the tetraethylammonium nitronate derived from 177 with aldehyde 178 provides anti-179 which then undergoes stereoselectively reduction (see Sect. 2.2.1) to provide -C-glycoside 180, intermediate in a synthesis of N-acetyl-neuraminic acid. 

The nucleophilic displacement efficacy of tetraethylammonium fluoride has been efficiently exploited in the preparation of 10 from the alcohol 9 via its trifluoromethanesulfonate derivative.195... 

A different route to pyrones is the preparative electrochemical oxidation of enamines in acetonitrile in the presence of tetraethylammonium perchlorate (88MI2) (Scheme 46). The synthesis of 2-pyrone derivatives has been carried out by reaction of /3-dicarbonyl compounds with methyl-a-benzoylamino-/3-dimethylaminoacrylate (96JHC751). Thiapyran derivatives can be obtained by interaction of enamines based on (/3-amino-a-cyanoacryloylmethyl)pyridinium chloride derivatives with carbon disulfide (95M711).The synthesis of pyridine derivatives based on analogous enamines has been described as well (95M711). 

Total hydrolysis of the polymers gave D-glucose only. Water-soluble derivatives (ethyl or carboxymethyl ethers) of the polymers were unaffected by a-amylase, but were partially hydrolyzed by a ceUulase preparation from Acdobader xylinum. The optical rotations of several preparations of this polyglucose and of cellulose (P 1150) in tetraethylammonium hydroxide were all 0°, thereby strongly suggesting that the polyglucoses are /S-D-linked.109... 

When the secondary reaction cycle shown in Scheme 6D.3 was discovered, it became clear that an increase in the rate of hydrolysis of trioxogly colate 10 should reduce the role played by this cycle. The addition of nucleophiles such as acetate (tetraethylammonium acetate is used) to osmylations is known to facilitate hydrolysis of osmate esters. Addition of acetate ion to catalytic ADs by using NMO as cooxidant was found to improve the enantiomeric purity for some diols, presumably as a result of accelerated osmate ester hydrolysis [16]. The subsequent change to potassium ferricyanide as cooxidant appears to result in nearly complete avoidance of the secondary cycle (see Section 4.4.2.2.), but the turnover rate of the new catalytic cycle may still depend on the rate of hydrolysis of the osmate ester 9. The addition of a sulfonamide (usually methanesulfonamide) has been found to enhance the rate of hydrolysis for osmate esters derived from 1,2-disubstituted and trisubstituted olefins [29]. However, for reasons that are not yet understood, addition of a sulfon-amide to the catalytic AD of terminal olefins (i.e., monosubstituted and 1,1-disubstituted olefins) actually slows the overall rate of the reaction. Therefore, when called for, the sulfonamide is added to the reaction at the rate of one equivalent per equivalent of olefin. This enhancement in rate of osmate hydrolysis allows most sluggish dihydroxylation reactions to be mn at 0°C rather than at room temperature [29]. 

Ceramides prepared in this way have been used for the partial synthesis of the a-L-fucopyranosyl ceramide (84) (a compound previously isolated from metastatic human carcinoma). Condensation [88] of 2,3,4-tri-Obenzyl-a-L-fucopyranosyl bromide (80) with an unprotected ceramide in the presence of tetraethylammonium bromide in di-chloromethane and subsequent chromatographic purification gave (81) which on catalytic hydrogenation gave the saturated fucosyl ceramide (84). The dichloroacetamido derivative (82) was prepared similarly and converted into the free sphingosine derivative (83) by the action of barium hydroxide. 

Ozaki and co-workers <1998TL8121> applied an electrochemical method for the synthesis of thietanes by the electroreduction of the acetylenic derivative of thioacetic acid 52. The electrochemical reaction was carried out in dimethylformamide (DMF) using tetraethylammonium perchlorate as a supporting electrolyte at a graphite plate electrode in the presence of an N,N -bis(salicylaldehydo)ethylenediamine (salen) nickel complex 54 (Equation 19). The desired 2-benzylidene-4-ethyl-thietane 53 was obtained in fair yield. 

The oxidation of the nor-reticuline derivatives (40a) and (40b), using a variety of tetraethylammonium diacyloxyiodates as oxidizing agents, supplied good yields of the norisoboldines (41a) and (41b).46a This marks the first recorded use of diacyliodates for the synthesis of aporphines. 

Both thiourea (tu) and thiosemicarbazide (tsc) are bifunctional ligands, containing a DD face in addition to one or two co-ordination sites. The reaction of [Zn(tu)4]2+ with a dicarboxylate normally occurs with displacement of thiourea to give coordination polymers of the type [Zn(tu)2(p-dicarboxylate)] in which the chains are cross-linked by DD-AA interactions [157]. The fumarate derivative contains identical inter-plane hydrogen bonding to that observed in (NEt4)2 [fumarate] 2tu [158], in which the zinc atom has formally been replaced by two tetraethylammonium cations. 

Initially it was believed that this anomalous behaviour was linked to the rotation of a tetraethylammonium guest within the capsule which has been observed. This proved not to be the case, as was confirmed by the use of lower symmetry calixarene derivatives to reduce the ambiguity of the NMR spectra. Molecular dynamics calculations were employed to show that the size of the tetraethylammonium guest means that the capsule has to be significantly expanded in order for it to fit within the cavity. The result of this expansion is that the ureas are only... 

Catalyst retention can be further optimised if a charged derivative of the (QN)2PHAL-ligand is used. Quatemisation of one of the nitrogen atoms with benzyl bromide affords the cationic ligand (QN)(QN-Benz)PHAL, and indeed recyclability was improved in the presence of this ligand, however at the cost of lower ee, as shown in Scheme 5.14.[66] The addition of one equivalent of tetraethylammonium acetate was found to improve the selectivity. 16 11... 

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