Biphenyl derivatives, conversion

Another way to produce biphenyl derivates using flow was described by Leeke et al. [34] where they performed a Pd catalyzed Suzuki-Miyaura synthesis in the presence of a base. First experiments were carried out in toluene/methanol solvent. A reaction mixture was passed through the encapsulated Pd filled column bed length 14.5 cm (some cases 10 cm) x 25.4 mm id. 45 g of PdEnCat. Base concentration, temperature and flow rate were optimized and at optimum parameters (0.05 M base concentration, 100°C and 9.9 mL/min) the conversion was 74%. Then the reaction was performed under supercritical conditions using supercritical CO2 at high pressure and temperature. After optimizing the concentration of base, flow rate, pressure and temperature, the highest conversion rate (81%) was observed at 166 bar and 100°C where the reactant mixture was monophasic in the supercritical state. This system is able to produce 0.06 g/min of the desired product. 

Electrophilic attack by the ortho heteroatom of biphenyl derivatives is involved in the conversions (22 - 23) (82JOC3585) and (24 — 10) (62JOC4111). 

The action of concentrated sulfuric acid at 0 °C on the geminal diazide 2 gives in high yield (> 90 %) the N-oxamoyl anthranilic acid 14 [72TH000], This compound can be further hydrolyzed to anthranilic acid 15 or converted into the ester 16. N-Alkyl derivatives of 2 behave in a similar manner cf. the conversion of 18 to 19. The latter compound may be easily degradated to 1,2,3,4-tetrahydroquinoline-l-carboxylic acid in the same way. Only the biphenyl derivative of 2 reacts differently and affords acridone 17 in 65 % yield. The cleavage of the C-3 - C-4 bond in these reactions is again noteworthy. 

Shi and Wan report that the three biarylmethyl alcohols (161), (162) and (163) undergo conversion into the corresponding pyrans (164), (165) and (166) on irradiation at 254 nm in acetonitrile or acetonitrile/water. The reaction involves the conversion of the diols into the corresponding quinone methide for example, (167) is formed from (161) by formal loss of water. Cyclization of this quino-methide intermediate affords the final products. Previously Wan and his coworkers have described this reactivity for biphenyl derivatives. The quantum... 

Another approach is to conduct competitive experiments with binary mixtures in which the complete reaction pathway is developed according to a reaction scheme like that of Scheme 1 described in the beginning of this review or like those shown in Figs. 12-15. Much of the confusion found in past reports of the kinetics of dibenzothiophene and its alkylated derivatives has come from incomplete deconvolution of the reaction network. Selectivity is often reported as the ratio of the yields of biphenyls (direct sulfur extraction) to the yields of cyclohexylbenzenes (hydrogenative route). As discussed in Section IV, cyclohexylbenzenes are produced via two different routes and, unfortunately, even low-conversion studies do not circumvent this confusion. To illustrate how conclusions can often be confused if the wrong model is used, some examples of reported competitive inhibition experiments will be discussed. 

One process which is related to the photocyclization of stilbene-like substrates is the conversion of 2-vinyl biphenyls to 8,9a-dihydrophenanthrenes, which undergo a facile thermal isomerization to 9,10-dihydrophenanthrenes (Scheme 9.24) [36]. For the synthesis of 5,6-dihydro- 1,10-phenanthroline and 1,10-phenanthroline derivatives, metal-chelation of the nitrogen atoms has shown to be productive (Scheme 9.25) [37]. 

Several routes to carbazoles featuring formation of two CN bonds rely on transition metal-catalyzed amination reactions . Such a methodology has been employed in the conversion of the biphenyl 26 into the carbazole 27 (Scheme 11). Variation of the amine and biphenyl components allowed preparation of a series of carbazole derivatives bearing either electron-withdrawing or releasing substituents <2003AGE2051>. Likewise, the triflate 28 could be efficiently transformed into a similar tricyclic system 29 by amination with aniline (Scheme 12) <2005AGE4036>. 

Several derivatives of phenols have been found to be especially suited for hydrogenolysis by catalytic hydrogenation. Phenol ethers prepared by the reaction of phenols with l-phenyl-5-chlorotetrazole or with 2-chlorobenzoxazole are hydrogenolyzed over 5% palladium on carbon or over platinum oxide, but not over Raney nickel. The hydrogenations are run at 35 °C in benzene, ethanol or tetrahydrofuran, and give 35-89% yields of the corresponding hydrocarbons. The reaction sequence is exemplified by conversion of phenylphenols to biphenyls (equation 77). 

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