Hexasubstituted aromatic

In 1990, Nakamura et al. reported for the first time the complete biosynthetic origin of the whole carbon skeleton of carbazomycin B isolated from lower plants (378). Based on feeding experiments with and C-labeled compounds, followed by measurement of radioactivity and C-NMR spectroscopy, it was shown that L-tryptophan (408) contributes to C-3 and C-4 of the hexasubstituted aromatic ring, in addition to the indole ring, indicating tryptophan as the progenitor of carbazomycin B (261), in contrast to Chakraborty s proposal of 2-methylcarbazole. The indole part of L-tryptophan (408) is formed by incorporation of two carbons from phosphor-ibosyl diphosphate (430), with loss of the anthraniiic acid (397) carboxyl. The... 

Jung, M.E. and Siedem, C.S. (1993) Efficient synthesis of a hexasubstituted aromatic ring via an intramolecular MichaeL-Aldol process preparation of a late tricyclic intermediate for the synthesis of pseudopterosin A./. Am. Chem. Soc., 115, 3822-3823. 

Under the conditions of Figure 12.12 acetophenone yields 1,3,5-triphenylbenzene. Lewis rather than Bronsted acids initiate the cyclodehydration of ketones to give aromatic compounds in an analogous fashion. Under influence of titanium tetrachloride and zinc chloride the steroid coprostanone, for example, leads to the formation of hexasubstituted benzene the 3x3 cyclohexane chairs that constitute the substituents of the resulting benzene ring are rigid... 

The adduct is similar to the one formed during an electrophilic aromatic substitution reaction. Even though there is the loss of the aromatic delocalisation, the resultant radical is itself delocalised to some extent. Once formed, such aromatic radicals may then react in a number of different ways. It is possible for two to dimerise or disproportionate. Alternatively, such a radical may undergo an overall substitution after the abstraction of a hydrogen atom, or even react further to result in overall addition. If the last option is followed, then often addition takes place at all three double bonds to give the hexasubstituted product, C6H6X6. 

Irradiation of the biscyclopropenylmethane la in the presence of thioxanthone as a triplet sensitizer gave tetraphenylbicyclo[2.2.1]heptadiene 3a by bond relocation in an intermediate strained quadricyclane 2a.A similar cyclization occurred for the 1,2-biscyclo-propenylethane derivative lb, while in the case of 4 aromatization was observed either on photolysis in diethyl ether or thermolysis for 24 hours at 175 C. In the same manner, the sulfone 5 was converted into a hexasubstituted benzene. ... 

The precursor of the hexasubstituted benzene in jatropholone A and B was a Diels-Alder adduct formed when furan 190 and enone 191 were reacted under high pressure. Subsequent aromatization was initiated by treatment with dilute hydrochloric acid,Eq. 120 [177]. This strategy was also used to install the aromatic ring in the syntheses of mansonone E [178]. 

The hexasubstituted benzenoid compound (145) is synthesized in one step by the condensation of 2 mol of the dienol silyl ether (146) with 1 mol of methyl orthoacetate and TiCU. The reaction is believed to proceed through the intermediate (147). Compound (147) can be considered as a potential 1,3,5-trielectrophile. The more reactive sites in (147) are at C-5 and at C-3 respectively. Condensation of (147) with a second mole of (146) gives therefore regioselectively the aromatic compound (145). By this method, the plant growth substance sclerin (148) can easily be prepared. 

Many weak combination and overtone absorptions appear between 2000 and 1667 cm The relative shapes and number of these peaks can be used to tell whether an aromatic ring is mono-, di-, tri-, tetra-, penta-, or hexasubstituted. Positional isomers can also be distinguished. Since the absorptions are weak, these bands are best observed by using neat liquids or concentrated solutions. If the compound has a high-frequency carbonyl group, this absorption will overlap the weak overtone bands so that no useful information can be obtained from the analysis of the region. 

The applicabihty of Turbo-Hauser A towards aromatic substrates is expertly proven by the susceptibility of the substituted aromatic ethyl 3-chlorobenzoate to undergo four consecutive direct magnesiations/electrophilic quenches to yield a hexasubstituted benzene derivative (Fig. 12) [30]. The second metallation requires careful choice of solvent in neat THF a competitive deprotonation occurs in a 90 10 ratio in favour of the desired product, which can be improved to a near quantitative level of 98.5 1.5 ratio by employing the less polar THF/Et20 (1 2) mixture. It should also be noted that the third and fourth metallations must be carried out at 50 °C, reflecting the greater sensitivity of the multi-functionalised benzenes. 

A multiple functionalization of a bisubstituted aromatic compound such as 68 can be achieved by successive magnesiation with TMPMgCl-LiCI (64) and quenching with various electrophiles, finally leading to hexasubstituted benzene derivatives such as 70-73 (Scheme 2-29). i... 

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