O-aryl

To minimize racemization, the use of nonpolar solvents, a minimum of base, low reaction temperatures, and carbamate protective groups (R = O-alkyl or O-aryl) is effective. (A carbamate, R = O-r-Bu, has been reported to form an oxazolone that appears not to racemize during base-catalyzed coupling.) ... 

To minimize racemization, the use of nonpolar solvents, a minimum of base, low-reaction temperatures, and carbamate protective groups (R = O-alkyl or O-aryl) are effective. 

O-Alkyl-7 und O-Aryl-hydroxylamine8 lassen sich mit Lithiumalanat in die Komponenten spalten bzw. re-duktivumlagern , O-Acyl-10bzw. N-Sulfonyl-hydroxylamine11 imerstenSchritt zum Hydroxylamin und Al-kohol bzw. Sulfonamid reduzieren. 

Aminocarbonyl-phenyI)- 683 O-Aryl 481 (Aryloxy-phenyl)- 684 N-Benzyl- 374f., 614... 

In the case of triptycene derivatives such as 121, a complete 360° rotation of the aryl group around the O—aryl bond requires the aryl group to pass over three rotational... 

H NMR spectroscopy studies of iron(IIl) a-alkyl and o-aryl porphyrins have been very important in elucidating spin states. Alkyl and most aryl complexes with simple porphyrin ligands (OEP, TPP, or TTP) are low spin, S — I /2 species. NMR spectra for the tetraarylporphyrin derivatives show upheld resonances for the porphyrin pyrrole protons (ca. — 18 to —35 ppm), and alternating upfield and downfield hyperfine shifts for the axial alkyl or aryl resonances. For -alkyl complexes, the a-protons show dramatic downfield shifts (to ca. 600 ppm), upfield shifts for the /3-protons (—25 to — 160 ppm) and downfield shifts for the y-protons (12 ppm). The cr-protons of alkyliron porphyrins are not usually detected as a result of their large downfield shift and broad resonance. These protons were first detected by deuterium NMR in the dcuterated complexes Fe(TPP)CD3 (532 ppm) and Fe(TPP)CD2CDi (562, -117 ppm). ... 

Hydroxydearyloxy Substitution + O-Aryl, O-Alkyl Substitution Hydrolysis and Transglycosylation... 

Chloroquinoxaline and hydroxylamine hydrochloride (0.5 equiv) gave 2-(quinoxalin-2-yloxyimino)-l,2-dihydroquinoxaline (169) (Me2SO, Na2C03, 20°C, 24 h >80%, in two polymorphic forms, checked by X-ray analysis the mechanism clearly involved rapid aminolysis followed by O-arylation).941... 

The formation of these compounds has been rationalized according to Scheme 6. The reaction of Os (E )-CH=C 11 Ph C1 (C())( P Pr3)2 with n-BuLi involves replacement of the chloride anion by a butyl group to afford the intermediate Os (/i> CH=CHPh ( -Bu)(CO)(P Pr3)2, which by subsequent hydrogen (3 elimination gives OsH ( >CI I=CHPh (CO)( P Pr3)2. The intramolecular reductive elimination of styrene from this compound followed by the C—H activation of the o-aryl proton leads to the hydride-aryl species via the styrene-osmium(O) intermediate Os r 2-CH2=CHPh (CO)(P Pr3)2. In spite of the fact that the hydride-aryl complex is the only species detected in solution, the formation of OsH ( )-CH=CHPh L(CO)(P Pr3)2 and 0s ( )-CH=CHPh (K2-02CH)(C0)(P,Pr3)2 suggests that in solution the hydride-aryl complex is in equilibrium with undetectable concentrations of OsH ( )-CH=CHPh (CO)(P,Pr3)2. This implies that the olehn-osmium(O) intermediate is easily accessible and can give rise to activation reactions at both the olefinic and the ortho phenyl C—H bonds of the... 

Chiou et al. (1998) attributed the enhanced partitioning of PAHs with respect to other HOCs to relatively high compatibility between the cohesive energy densities of PAHs and the aromatic components in SOM. However, the difference in Koc values between soils and sediments is related to the difference in polar group, rather than aromatic carbon, contents (Kile et al. 1999). The authors concluded that the content of polar groups (O-aryl and carboxyl C) has a large negative influence on Koc values, and hence on HOC sorption in soil and sediment. 

A combination of the SNAr feature and the coordination ability of a copper complex has led to the development of a new O-arylation method that makes use of a triazene as an activating and directing group (Equation (2)).32,33 This protocol, though necessitating a three-step removal sequence of the triazene moiety, has been successfully applied to the total synthesis of vancomycin1 6 and extended to a solid-phase synthesis in which the triazene unit serves as an anchor to the resin.37... 

Commensurately with the development of various catalyst systems, the Pd-catalyzed G-O cross-coupling has found a number of synthetic applications. Examples include the syntheses of the protein kinase G (PKC) activator (+)-decursin,104 the natural product heliannuol E,105 a chiral 2-methyl chroman,106 and a series of aryloxy and alkoxy porphyrins.107 The Buchwald-Hartwig coupling has also been utilized in the preparation of a heterocycle library.108 Intramolecular O-arylation has also been achieved in the reactions of enolates with aryl halides leading to benzofur-ans.109,110 Finally, a double cross-coupling between an 0-dibromobenzene and a glycol has also been applied for the preparation of benzodioxanes (Equation (16)).1... 

Fig. 9 A hypothetical More-O Ferrall Jencks diagram for the attack of methoxide on O-aryl phosphate triesters (20) and 5-aryl phosphorothioates (21). Note that the diagram for attack of a metal-coordinated methoxide would be similar, but Mx +-coordination would push the TS toward the S-corner, possibly stabilizing the pentacoordinated intermediate to the point that the reaction occurs stepwise with the likely rate-limiting step being breakdown.

Sn2 reactions of glycosyl iodides have proven especially advantageous in the synthesis of 2-deoxy P-O-aryl-D-glycosides. This is a challenging linkage to make, as there is no neighboring group to participate. Sometimes, stereochemistry is... 

The glycosylation based on the Mitsunobu reaction has been most commonly directed to the synthesis of O-aryl glycosides, a structural motif found in a variety of natural products [80-82], Early work by Grynkiewicz [83,84], among others [85-87], established the viability of triphenylphosphine and diethylazodicarboxylate to promote the glycosylation of phenol acceptors at ambient temperature. More recently, Roush and coworkers have discovered that the glycosylation performed well in the... 

Method A The glucopyranosyl bromide (1 mmol) in CH2C12 (10 ml) and HzO (10 ml) is added to the phenol (3 mmol) and TEBA-C1 or Adogen (0.2 mmol) in aqueous KOH or NaOH (25 mmol) and the mixture is stirred at room temperature for 8-60 h. The organic phase is separated, washed with H20, dried (MgS04), and evaporated to yield the O-aryl derivative (68% from phenol 60% from 2-cresol 53% from 3-chlorophenoI, 54% from 4-methoxyphenol 56% from 4-nitrophenol 57% from 1-naphthol 44% from thio-phenol 36% from 8-hydroxyquinoline). 

Diaryl benzenephosphonothioates (>80%) and 0,0-dimethyl O-aryl phos-phothionates have been synthesized under mild conditions from the reaction of phenols under basic two-phase conditions with benzenephosphonothioic dichloride and dimethyl phosphorochloridothionate, respectively [9, 10]. The reaction with the phosphorochloridothionate requires the catalytic effect of both tetra- -butylammo-nium bromide and A-methylimidazole for the rate to be sufficiently enhanced to make it a viable route to the ester [10]. 

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