2,2* Dihydroxybiphenyl complexes, with

Kodera and co-workers demonstrated348 that complex (400) (distorted TBP Cu-Cu 2.926 A 2/=—148 cm-1 they also characterized a closely similar ethoxy-bridged complex with two molecules of MeCN) catalyzes the quantitative oxidation of 2,4-di-tert-butylphenol to 3,3, 5,5 -tetra-tert-butyl-2,2 -dihydroxybiphenyl with H202. Krebs and co-workers provided models for the... 

Optically active 19a was previously obtained by inclusion complexation with N -benzylcinchon idi um chloride 21 [36], Compound 21 was also a very efficient resolving agent for rac-17 [37], Crystal structure analysis of a (1 1) complex of 21 and selectively included (+)-17 showed that the molecular aggregate was associated by formation of a Cl HO hydrogen bond. Racemic compound 20 could be efficiently resolved only by complexation with (R,R)-(—)-trans-2,3-bis(hydroxydiphenylmethyl)-l,4-dioxaspiro[4.4]nonane 3b. A crude inclusion complex of 1 1 stoichiometry of 3b was formed selectively with (+)-20 in a 2 1 mixture of dibutyl ether/hexane. One recrystallization from the above combination of solvents gave a 34 % yield of the pure complex. Optically active (+)-20 was obtained by dissolving the complex in 10% NaOH, followed by acidification with HC1 and then recrystallization. The optical purity determined by HPLC (Chiralpack As) was >99.9 %. As far as we know, this is the only report of the resolution of 4,4 -dihydroxybiphenyl derivatives. Conversely, an inclusion... 

Strecker reaction catalyzed by (i-PrO)4Ti whereby tosylimines accept Me3SiCN enantio-selectively is achieved by modifying the environment surrounding the metal center by alkoxy group exchange with 3,3 -di(P-naphthyl)-2,2 -dihydroxybiphenyl, and further complexation with cinchonine. ... 

Figure 13 Structures of the active sites of (a) 2,3-dihydroxybiphenyl 1,2-dioxygenase complexed with catechol (PDB IKND) (b) deacetoxycephalosporin synthase with bound a-ketoglutarate (PDB IRXG) (c) isopenicillin N synthase with coordinated substrate and NO (PDB IBLZ) (d) naphthalene dioxygenase with bound dioxygen in the presence of substrate (not shown) (PDB 107M).

Figure 29. Structures and distances between the Fe ion and the ligated atoms in the native Bph C enzyme (a) and its complex with 2,3-dihydroxybiphenyl (2,3-DHBP) (b) [394].

Abstract. Novel macrocyclic compounds, hexahydroxy[1.0.1.0.1.0]- (2b) and octahydroxy[1.0.1.0.-1.0.1. OJmetacyclophane (2c) have been prepared in 50-70% yield by base-catalyzed condensation of 5,5 -di-rerr-butyl-2,2 -dihydroxybiphenyl (1) with formaldehyde in refluxing xylene. An attempted alkylation of the flexible macrocycles 2b and 2c with ethyl bromoacetate in the presence of CS2CO3 under acetonitrile reflux gave only one pure stereoisomer 3 and 4, respectively, while other possible isomers were not observed. The structural characterization of these products is also discussed. The two-phase solvent extraction data indicated that hexaethyl ester 3 and octaethyl ester 4 show strong metal affinity, comparable with that of the corresponding calix[n]arenes, and a high K" " selectivity was observed for octaethyl ester 4. H-NMR titration of hexaethyl ester 3 and octaethyl ester 4 with KSCN clearly demonstrate that a 1 1 complex is formed which is stable on the NMR time scale. 

A charge transfer complex is involved in the photochemical reaction between 4-cresol and tetranitromethane. Irradiation at 350 nm yields the o-nitrated product 235 ° . Other phenols such as phenol, 2- and 4-chlorophenol and 2- and 4-cresol behave in a similar manner and irradiation yields 2- and 4-nitrated products (236, 237) ° . The quantum yields for product formation are in the range 0.12-0.31. Only the formation of 3-nitrophenol from phenol is inhibited, as might be expected from attack at the 3-position, and shows a low quantum yield. It has been reported that 2-hydroxy- or 4-hydroxybiphenyl and 4,4 -dihydroxybiphenyl are the primary products formed from the photochemical reaction of biphenyl with sodium nitrate in aqueous methanol . Apparently the hydroxybiphenyls are prone to undergo photochemical nitration as a secondary process and yield the biphenyls 238 and 239 as well as 4,4 -dihydroxy-3,3 -dinitrobiphenyl, originally reported by Suzuki and coworkers under heterogeneous conditions. 

H0)2As=0 rather than an intermediate complex, as found for the reaction with chromic acid. Cyclic esters, e.g. (134), can be obtained from arsenic trichloride and 2,2 -dihydroxybiphenyl, and when the reaction with pyro-... 

The oxidative dimerization of dialkylphenols proceeds in the presence of immobilized Cu(Il) complexes. One-electron reduction of the Cu(II)-phenolate formed results in the production of a phenoxy radical which is oxidized via the intermediate dihydroxybiphenyl to diphenoquinone. At the same time the active centers are regenerated by oxidation of the Cu(I) formed to Cu(II) (the ping-pong mechanism). Such cycles - reduction of metal ions at the stage of the reaction with the substrate and its reoxidation by molecular oxygen - are often observed. 

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