Tetrahydrofurans Subject

Cytochalasin B (from dehydrated mould matter) [14930-96-2] M 479.6. Purified by MeOH extraction, reverse phase Cl8 silica gel batch extraction, selective elution with 1 1 v/v hexane/tetrahydrofuran, crystn, subjected to TLC and recrystallised [Lipski et al. Aruil Biochem 161 332 1987]. 

The outcomes of intramolecular cyclizations of hydroxy vinylepoxides in more complicated systems can be difficult to predict. In a study of the synthesis of the JKLM ring fragment of dguatoxin, epoxide 44 was prepared and subjected to acid-mediated cydization conditions (Scheme 9.24) [114]. Somewhat surprisingly, the expected oxepane 45 was not formed, but instead a mixture of tetrahydropyran 46 and tetrahydrofuran 47 was obtained, both compounds products of attack of the C6 and C5 benzyl ether oxygens, respectively, on the allylic oxirane position (C3). Repetition of the reaction with dimsylpotassium gave a low yield of the desired 45 along with considerable amounts of tetrahydropyran 48. 

The important observation from the data in Table 3 is that NC samples subjected to acid bod followed by tetrahydrofuran (THF)-benzene treatment yielded essentially the same sulfate contents as samples subjected to THF-benzene treatment alone. From this the authors interpret that sulfate contents from THF-benzene treatments actually represent absolute values of the difficult-to-remove sulfate which may very well be true sulfate ester . It is also tentatively concluded that approximately 90% of the original sulfate content in unstabilized NC is readily removable sulfuric acid with the remainder the more difficult-to-remove sulfate ester. Dilute acid boil treatment of NC for 56 hours does not eliminate all of the free sulfuric acid and leaves the difficult-to-remove sulfate practically unchanged... 

The synthesis of tetrahydrofuran derivatives from unsaturated alcohols via hydroformylation intermediates was developed many years ago. Moderate yields are obtained from but-2-en-l,4-diol (Scheme 54)94 but hydroformylation is not the major pathway when coniferyl alcohol is subjected to the oxo process (Scheme 55).9S A more complicated reaction is involved... 

Apart from the qualitative observations made previously about suitable solvents for study, the subject of solvates has two important bearings on the topics of thermochemistry which form the main body of this review. The first is that measured solubilities relate to the appropriate hydrate in equilibrium with the saturated solution, rather than to the anhydrous halide. Obviously, therefore, any estimate of enthalpy of solution from temperature dependence of solubility will refer to the appropriate solvate. The second area of relevance is to halide-solvent bonding strengths. These may be gauged to some extent from differential thermal analysis (DTA), thermogravimetric analysis (TGA), and differential scanning calorimetry (DSC) solvates of "aprotic solvents such as pyridine, tetrahydrofuran, and acetonitrile will give clearer pictures here than solvates of "protic solvents such as water or alcohols. 

Although aldehydes obtained through the hydroformylation of dihydrofurans are interesting building blocks for organic synthesis, few studies have been reported on the subject. In 1998, previous work on the control of the regio-selectivity in the hydroformylation of dihydrofurans has been reported with rhodium systems modified with different ligands [77,78]. In the hydroformylation of 2,5-dihydrofuran 46 the expected product is the tetrahydrofuran 3-carbaldehyde 49 (Scheme 7). 

A. ( )-1-(Dimethylphenylsilyl)-1-buten-3-ol (2a). A solution of 10.0 g (0.143 mol) of racemic 3-butyn-2-ol (Note 1) dissolved in 255 mL of tetrahydrofuran (THF, Note 2) in a 1-L, round-bottomed flask equipped with a reflux condenser and nitrogen atmosphere is prepared. Dimethylphenylsilane (21.4 g, 0.157 mol) (Note 3) and a small piece of sodium metal (ca. 5 mg) (Note 4) are placed in the reaction mixture. The solution is stirred for 15 min and 12 mg (2.05 x 10 5 mol) of bis(q-divinyltetramethyldisiloxane)tri-tert-butylphosphineplatinum(O) (Note 5) is added. The reaction mixture is then heated under reflux for 12 hr. The orange solution is cooled to ambient temperature, and the solvent is removed under reduced pressure to yield a crude orange residue containing 2a. The oil is subjected to column chromatography on silica gel (Note 6) (gradient elution 5, 10, 20, 35% EtOAc/hexanes) providing 25.4 g (123.23 mmol, 86%) of pure 2a as a yellow oil (Note 7). 

In contrast to the relative chemical stability of mono-epoxides, diol epoxides of fatty acids (10.52), which are formed from di-epoxides by EH, are subject to a different fate. In such metabolites, intramolecular nucleophilic substitution may occur, such that oxirane opening is accompanied by formation of a tetrahydrofuran ring [134], Such reactions of intramolecular nucleophilic substitution are discussed in detail in Sect. 11.9. In the case of diol epoxides of fatty acids, the resulting tetrahydrofuran-diols (10.53) are part of a much larger ensemble of oxygenated metabolites of fatty acids, the potential cytotoxicities of which are being evaluated [135]. 

One fact to keep in mind with such phases is that weak acid cation-exchange materials based on carboxylic acid functional groups are subject to esterification in the presence of alcohol containing eluents. Even thongh typical eluent conditions (i.e., weakly acidic aqneous eluents containing alcohol) do not favor ester formation, such stationary phases typically exhibit slowly declining capacity when operated in the presence of alcohol-containing eluents. Consequently, such columns are normally operated with acetonitrile, tetrahydrofuran or acetone rather than with methanol, in order to avoid this problem. 

For quality cured thermoset resins, approximately one percent of the mass is soluble when subjected to long-term leaching with tetrahydrofuran. Equilibrium is approached in two weeks resin swell is not visually noticeable. The monomeric, chemical structures are such that the hydrocarbon resins exhibit more pronounced viscoelastic properties whereas, the epoxy resins are similar to elastic bodies when subjected to tensile testing at room temperature. Therein, LRF 216 is less sensitive to flaws and is more nonlinear in tensile or compressive stress-strain analysis. 

System (4) has been reported for the quantitative determination of steroids in health and disease [143], Prior to analysis, free steroids were removed from the sample. Conjugated steroids were enzymatically hydrolyzed, and the liberated products extracted into 1 3 tetrahydrofuran-ethyl ether. The extract was evaporated, the residue dissolved in acetic acid, and then oxidized with sodium bismuthate. The final product was acetylated or formulated, and subjected to GC analysis along with the standard. A stabilized column of 4% LAC-2R-446 and 1% 85% phosphoric acid on... 

In general, simple alkyllithiums exist predominantly as either hexamers (for sterically unhindered RLi) or tetramers (for sterically hindered RLi) in hydrocarbon solvents and as tetramers in basic solvents (9-12). Polymeric organolithium compounds such as poly(styryl)lithium exist as dimers in hydrocarbon solution and are unassociated in basic solvents such as tetrahydrofuran (13-15). The state of association of poly-(dienyl)lithiums in hydrocarbon solution is a subject of current... 

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