Aryloxy groups

In the presence of sulfide or sulfhydryl anions, the quinonemethide is attacked and a benzyl thiol formed. The P-aryl ether linkage to the next phenylpropane unit is broken down as a result of neighboring-group attack by the sulfur, eliminating the aryloxy group which becomes reactive phenolate ion (eq. 2). If sulfide is not present, a principal reaction is the formation of the stable aryl enol ether, ArCH=CHOAr. A smaller amount of this product also forms in the presence of sulfhydryl anion. 

Related examples of silicon-containing titanocycles have also been prepared (282). These compounds are air-stable and not decomposed by methanol. When CpCpWiClOAr reacts with Grignard reagents, the aryloxy group is replaced by R, not by Cl (283). Compounds of the formula (Cp2TiR)20 prepared from (CP2TiCl)20 + RLi, where Ris CH, C2H, CgH, y)-tolyl, CgH CM2, or CH2=CH, are thermally stable and quite stable to air (283,284). 

If the rotational freedom of the aryloxy group is restricted, as in 4-[(arylsulfonyl)methyl]-2H-l-benzopyranes (55), the remote group interaction is not possible anymore and these derivatives fragment mainly by ejecting ArS02H and S0238 (equation 26). 

An example of this approach concerns the incorporation in the polymer of aryloxy groups. The two structures VI and VII have been synthesized both containing the same 50/50 molar ratio of aryloxy and oligoethyleneoxy groups. 

The diastereomerically pure chlorides 73a and 73b afforded the corresponding P-substitution products on reaction with nucleophiles. Thus 73a and 73b could be converted readily into the corresponding alkoxy-derivatives on treatment with an alcohol in the presence of triethylamine and into aryloxy-derivatives upon treatment with the sodium salt of the appropriate phenol at room temperature. Replacement of chlorine by an alkoxy- or aryloxy-group occurred with retention of configuration, e.g., 73a gave 74a, 75a, and 76a. Similarly, 74b and 75b could be obtained from 73b (Scheme 24) [32, 38, 54],... 

Of course, this thesis remains to be tested and probably can be confirmed or rejected through study of a series of close derivatives of HPNPP where the aryloxy group is varied which is currently underway in our laboratories.100... 

R2 halogen atoms, aryloxy groups, diene and/or iso- Catalyst (2,5-diphenylphospholyl (cyclopentadie- (Houston, USA) 36 (1992)... 

This now allows the calculation of EM for A.5.7 and A.5.8 using a correction factor of 10 for the decrease in reactivity expected when one spectator aryloxy group of a phosphate triester is replaced by an alkoxy group (Bromilow el al., 1972)... 

The chemical diversity of carboxylic acid esters (R-CO-O-R ) originates in both moieties, i.e., the acyl group (R-CO-) and the alkoxy or aryloxy group (-OR7). Thus, the acyl group can be made up of aliphatic or aromatic carboxylic acids, carbamic acids, or carbonic acids, and the -OR7 moiety may be derived from an alcohol, an enol, or a phenol. When a thiol is involved, a thioester R-CO-S-R7 is formed. The model substrates to be discussed in Sect. 7.3 will, thus, be classified according to the chemical nature of the -OR7 (or -SR7) moiety, i.e., the alcohol, phenol, or thiol that is the first product to be released during the hydrolase-catalyzed reaction (see Chapt. 3). Diesters represent substrates of special interest and will be presented separately. 

Other functionalized supports that are able to serve in the asymmetric dihydroxylation of alkenes were reported by the groups of Sharpless (catalyst 25) [88], Sal-vadori (catalyst 26) [89-91] and Cmdden (catalyst 27) (Scheme 4.13) [92]. Commonly, the oxidations were carried out using K3Fe(CN)g as secondary oxidant in acetone/water or tert-butyl alcohol/water as solvents. For reasons of comparison, the dihydroxylation of trons-stilbene is depicted in Scheme 4.13. The polymeric catalysts could be reused but had to be regenerated after each experiment by treatment with small amounts of osmium tetroxide. A systematic study on the role of the polymeric support and the influence of the alkoxy or aryloxy group in the C-9 position of the immobilized cinchona alkaloids was conducted by Salvadori and coworkers [89-91]. Co-polymerization of a dihydroquinidine phthalazine derivative with hydroxyethylmethacrylate and ethylene glycol dimethacrylate afforded a functionalized polymer (26) with better swelling properties in polar solvents and hence improved performance in the dihydroxylation process [90]. 

The subsitution of a hydrogen atom in a hydrocarbon by an alkoxy or aryloxy group (R-O/Ar-O) yields another class of compounds known as ethers , for example, CHgOCHg (dimethyl ether). You may also visualise ethers as eompounds formed by... 

Example 46 Dabkowski et al. have developed a very useful way of generating the P kp moiety by exchange of an aryloxy group attached to the P centre for a fluoride anion [31]. 

Aryloxy groups are much easier to displace compared to primary and secondary alkox-ide anions and so, aryl ethers are generally more useful in displacement reactions. Amine nucleophiles react with unsymmetrical aryl ethers to form the amine of the heavier nitrated moiety.Accordingly, 2,4,6-trinitrodiphenyl ether reacts with ammonia to expel phenoxide... 

Aryloxy groups have also been used as leaving groups. Reaction of 1-chloro- and l-methanesulfonyl[l,4]benzo-dioxino[2,3-r/]pyridazine 164 and 4-chloro[l,4]benzodioxino[2,3-Hpyridazine with NaOMe afforded ring-opened and cyclized pyridazines (Scheme 40). Their reaction with amines afforded 1-substituted [l,4]benzodioxino[2,3-rf]pyr-idazines 165, 4-substituted [l,4]benzodioxino[2,3-f]pyridazines 166, and/or 2-hydroxyphenoxypyridazines 167 (Scheme 41) <2004H(63)591>. 

In the thermal cyclization of 3-alkoxyphenyl A -(l-aryl-2,2,2-trifluoroethylidene)carbamates 287, obtained from 3-alkoxyphenols 285 and l-aryl-l-chloro-2,2,2-trifluoroethyl isocyanates 286, 2-aryl-2-trifluoromethyl-2,3-dihydro-477-l,3-benzoxazin-4-ones 290 were formed instead of the regioisomeric l,3-benzoxazin-2-ones 288 (Scheme 53). The formation of 290 was explained by a thermal isomerization of 287 involving a skeletal 1,3-rearrangement of the electron-rich aryloxy group to the azomethine carbon, which is electron deficient due to the electron-withdrawing CF3 group <2002JFC(116)97>. 

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