Hexa-substituted benzene derivatives

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. 

Not unexpectedly, 150 reacts with electrophilic reagents such as HC1, HBr and Br2, and also with H2 in a 1,4- fashion, to give the hexa-substituted benzene derivatives 153a and 153b (which are synthetic precursors of 150), 153c and 153d, respectively... 

Figure 4. Analogy in the topology of the ring in hexa substituted benzene derivatives and of the central ring in triphenylene, perylene, and coronene. (Only the ff electron structures are shown.)...

A thermal rearrangement of tetraarylated 6,6-dicyanopentafulvenes to hexa-substituted benzene derivatives has been reported to occur by a polar mechanism that leads to release of cyanide and supports the formation of both 1,3- and 1,4-dicyanobenzenes (Scheme 10... 

Dimethyl acetylenedicarboxylate (DMAD) (125) is a very special alkyne and undergoes interesting cyclotrimerization and co-cyclization reactions of its own using the poorly soluble polymeric palladacyclopentadiene complex (TCPC) 75 and its diazadiene stabilized complex 123 as precursors of Pd(0) catalysts, Cyclotrimerization of DMAD is catalyzed by 123[60], In addition to the hexa-substituted benzene 126, the cyclooctatetraene derivative 127 was obtained by the co-cyclization of trimethylsilylpropargyl alcohol with an excess of DMAD (125)[6l], Co-cyclization is possible with various alkenes. The naphthalene-tetracarboxylate 129 was obtained by the reaction of methoxyallene (128) with an excess of DMAD using the catalyst 123[62],... 

Ring fluorination is observed in reactions of protected aniline derivatives, with the ojp ratio of the products, e.g. 11-13, being dependent on the substituent 5 nitrobenzene is unreactive towards electrophilic substitution. The polymerization process may be studied by di-fluorobis(fluoroxy)methane reactions with variousfluoro-substituted benzene derivatives (hexa-... 

In the first case, the arms are grown from a single core with a given number of potentially active sites or a well-defined multifunctional initiator. In contrast to anionic multifunctional initiators, weU-defined soluble multifunctional cationic initiators are readily available. These multifunctional initiators with 3-8 initiating sites have been successfully applied for the synthesis of 3-8 arm star homo- and block copolymers of vinyl ethers, styrene and styrene derivatives, and IB. For example, six-arm star polystyrenes were prepared using initiator with six phenylethylchloride-type functions emanating from a central hexa-substituted benzene ring [250]. By subsequent end functionalization, a variety of end-functionaUzed A or (AB) (see above) star-shaped structures can also be obtained. 

Transmetalation of Zirconated Compounds. The reaction of allylzirconation derivatives with allyl chloride can be catalyzed by CuCl to give stereodefined 1,4,7-trienes. Similarly, zirconacyclopentadienes react with 2 equiv of allyl chloride to give 1,4,6,9-decatetraenes in good yields. Reaction of zirconacyclopentadienes with alkynes such as dimethyl acetylenedicar-hoxylate can produce a hexa-substituted benzene ring system in the presence of CuCl/LiCl (eqs 34 and 35). ... 

Butyne trimerizes in the presence of aluminum chloride to give hexamethyl Dewar-benzene (W. Schafer, 1967). Its irradiation leads not only to aromatization but also to hexa-methylprismane (D.M. Lemal, 1966). Highly substituted prlsmanes may also be obtained from the corresponding benzene derivatives by irradiation with 254 nm light. The rather stable prismane itself was synthesized via another hydrocarbon, namely benzvalene, a labile molecule (T. J. Katz, 1971, 1972). 

The structural comparison (Fig. 3) with both the twofold tris(trimethylsilyl)methyl substituted acetylene and 1,4-benzene derivatives (Fig. 1) as well as with the literature data [6a] for hexa-kis(rm.butyl)disilane [6b] containing a SiSi bond elongated to 270 pm ( ), for the linear ( ) hexa-kis(rm.butyl)disiloxane [6c] or for di(tris(trimethylsilyl)silyl)zinc [6d] is based advantageously on a model in which the two substituent half-shells are separated along their central C3 axes by spacers of different lengths. 

FIGURE 18. He(I) spectra of (A) 2,3,5,6-tetrakis(trimethylsilylmethyl)benzene, (B) extended records 6.5 eV to 9.5 eV for 1,4-, 2,6-, 1,3,5- and hexa-substituted derivatives and (C) comparison of ionization energies IE1 2 with those of the corresponding methyl-substituted benzenes126... 

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