Hexakis benzenes, synthesis

Inositols, ie, hexaliydrobenzenehexols, are sugars that have received increasing study and are useful in the treatment of a wide variety of human disorders, including vascular disease, cancer, cirrhosis of the Hver, frostbite, and muscular dystrophy (269). Myoinositol esters prepared by reaction with lower fatty acid anhydrides are useful as Hver medicines and nonionic surfactants the aluminum and ammonium salts of inositol hexasulfate are useful anticancer agents (270). Tetraarjloxybenzoquinones are intermediates in the preparation of dioxazine dyes (266,271). The synthesis of hexakis(aryloxy)benzenes has also beenpubUshed (272). 

In the early work, benzene formed the basis of a variety of multi-armed structures. Analogs bearing from 2—6 arms were prepared and compared for cation binding ability. The only indication of mode of synthesis for the hexa-substituted benzene derivative is that it was obtained on reaction of benzene-hexakis(methanethiol) and l-bromo-3,6,9-trioxatridecane . The reaction is illustrated in Eq. (7.6), below, devoid of reaction conditions and yields which were not specified. 

Hexa(oligophenyl)benzenes (e. g. 31 or 33) present one possible approach to the realization of this aim. Two efficient synthetic routes have been elaborated for the preparation of hexa(terphenyl)- and hexa(quaterphenyl)benzene. The first, involving palladium-catalyzed trimerization of diarylacetylenes [54] as the key step, was demonstrated by the synthesis of a hexakis-alkylated hexa(terphenyl)benzene derivative 31 from the corresponding bis(terphenyl) acetylene (32). The peripheral tert-alkyl substituents serve to solubilize the molecule. 

We are mainly concerned here with general processes but two specific reactions are of some interest. Fragmentation occurs in the pyrolysis of CFBrs, giving perfluorobenzene (Figure 9.3) [3-5] this was probably the first synthesis of this compound, although it was not reported for some time. Trimerisation of hexafluoro-2-butyne leads to hexakis(trifluoro-methyl)benzene [6,7], areaction that was referred to in Chapter 7, Section lllB, Subsection 1. 

Sequential functionalization of pyrazole-l-oxides via regioselective metallation led to the synthesis of 3,4,5-trisub-stituted-l-hydroxypyrazoles <2002JOC3904>. 3-Acylated-2-(4-methoxybenzyl)-2//-pyrazole 1-oxides were formed by the reaction between a 3-magnesium 2//-pyrazole-l-oxide and acid chlorides <2002J(P1)428>. 3-Arylated-l-hydroxypyrazoles were synthesized from 3-metallated-pyrazole 1-oxides <2001JOC8654>. The reaction between hexafluorobenzene and the anion of 1-hydroxypyrazole affords a mixture of the products of bis-, tetrakis-, and hexakis-substitution <2004ARK100>. In the case of hexakis(bromomethyl)benzene, its reaction with 1-hydroxy-pyrazole leads to the hexakis-substituted product. 

Binger reported the first synthesis of the derivative l,3,4,5-tetraethyl-2,3-dihydro-2-methyl-l//-l,3-diborole, which involved thermolysis of m-3,4-diethyl-3,4-bis(diethylboryl)hexane at 160 °C <1968AG288>. Recently, Siebert and co-workers heated hexakis(diethylboryl)benzene S3 at 180°C in a stream of argon and isolated l,2,3,4-bis(l, 3 -diborole-2, 3 -dihydro)-5,6-bis(boryl)benzene 21, accompanied by evolution of ethane (Equation 6) <2000EJI1177>. This compound represents the first example of a benzo derivative with two condensed 1,3-diborole rings. 

Interest in metal complexes containing polyfluoroalkyl- and polyfluoro-aryl-acetylenes as ligands has continued to be high, and has included compounds of platinum, palladium, gold, iridium, rhodium, - ruthenium, cobalt, - - nickel, molybdenum, and iron. These are reviewed in detail elsewhere in the Report (see Chapter 5). Such complexes may acquire usefulness for organic synthesis in due course thus significant amounts of hexakis(trifiuoromethyl)benzene are formed when perfluorobut-2-yne is incorporated into certain cobalt and nickel complexes. Similarly, the interesting compound hexakis(pentafluorophenyl)benzene was isolated in 40—70% yield hy trimerization of perfluorodiphenylacetylene over 7C-cyclopentadienylrhodium dicarbonyl in toluene. ... 

In 2006, the same group reported the synthesis of novel hexadentate imidazolium salts (Scheme 7.11) from hexakis(bromomethyl)benzene and 1-substituted imidazole and decided to evaluate their efficiency in the arylation of aldehydes with arylboronic acids [18]. The cattJyst generated in situ from the hexadentate imidazolium sailts and [Rh(COD)Cl]2 represents an easy-to-handle and high-yielding procedure for the addition of arylboronic acids to aldehydes. Luo and coworkers [19] then reported a new catalytic system on novel chiral imidtizolium salts and a stable NHC-Rh complex derived from L-proline (see Scheme 7.11). Excellent yields were achieved, but, unfortunately, their attempt to undergo an efficient asymmetric reaction failed, as a maximum enantioselectivity of 21% ee was achieved. 

SYNTHESIS AND STRUCTURE OF HEXAKIS(p-HYDROXYPHENYLOXY)BENZENE A VERSATILE ANALOGUE OF THE HYDROGEN-BONDED HEXAMERIC UNIT OF 3 HYDRO-QUINONE... 

Scheme 9. Synthesis of hexakis[(alkoxyphenoxy)me-thyl]benzenes [28].

Scheme 10. Synthesis of hexakis(alkylsulfone) derivatives of benzene [29]. Reagents (a) RSNa/HMPT 80-95% (b) m-CPBA/CHCIs 60-70%.

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