Tetracyclic hydrocarbons

The important bluish mixing component 11.22 for whitening polyester is made by Friedel-Crafts acylation of pyrene (Scheme 11.17). This tetracyclic hydrocarbon is not unlike anthracene in its susceptibility to substitution reactions. The most stable bond arrangement in pyrene appears to be that shown as form 11.47a, which contains three benzenoid (b) rings. Canonical form 11.47b, containing only two such rings, contributes to a lesser extent (Scheme 11.18). In all monosubstitutions, pyrene is attacked initially at the 3-position, corresponding to the a-positions in anthracene or naphthalene. 

C Me )2Sm]2C (C6H )2 reacts with CO in a remarkably facile stereospecific synthesis of a tetracyclic hydrocarbon (67) (Equation 9). 

The PE spectra of cyclobutadiene 281192, tetra-t-butylcyclobutadiene 282193, 1,3,5-tri-t-butylpentalene 283194 and aceheptylene 284195, all of which are subject to second-order bond localization, have been described in the literature. Further examples are 1,3,5,7-tetra-t-butyl-s-indacene 285 (which exhibits a first double band 1,2 at I 2 = 6.75 eV, followed by two bands at I = 8.50 eV and I = 9.30 eV) and the tetracyclic hydrocarbon 1,3,6,8-tetra-t-butylpentaleno[2,l-a]pentalene 286 (the first two bands of which are observed at 6.40 eV and 7.65 eV)196. 

Figure 2.9. Further examples of covalent self-assembly of a tetracyclic hydrocarbon (top) the Ugi reaction (middle) atropine synthesis (bottom).

O-propargyl-2-iodophenol in the presence of a palladium catalyst and phenylzinc chloride (3.30.) led to the formation of the 3-alkylidenedihydrobenzofurane in good yield (c.f 3.26.),37 The use of norbomene as capture reagent under similar conditions led to the formation of benzofurane bearing a tetracyclic hydrocarbon substituent.38... 

A particularly interesting cyclization utilizes a propargylsilane group as a terminator for a biomimctic synthesis of a tetracyclic hydrocarbon (6) with a potential cortical side chain.5... 

Steroids are tetracyclic hydrocarbons that are much more common in eukaryotes than in prokaryotes. Cholesterol, the most prominent member of the steroid family, is an important component of many eukaryotic membranes (see chapter 17). In addition, it is the precursor of the other two major classes of steroids The steroid hormones and the bile acids (fig- 20.1). 

Finally, 2, 4-ethanoadamantane (25), recently found in petroleum 37),may also be prepared by rearrangement. In this case, however, the tetracyclic hydrocarbon, 26, which had originally been expected to rearrange to 25, gave only tricyclic alkyl-adamantanes via a ring opening disproportionation process 381. This side reaction... 

Finally, when the acetoxy diketone (XC) is catalytically reduced, the reduction product saponified, and the last substance reduced by Clemmensen s method, there is obtained a saturated tetracyclic hydrocarbon, Ci9H,2 (XCV) (20). 

Of the six purely-aromatic tetracyclic hydrocarbons, only chrysene, benz[a] anthracene and benzo[ft]phenanthrene possess even marginal activity but, as shown (Tables 4.1,4.2, and 4.3), many benz[a] anthracene derivatives are active, as are some benzo[c]phenanthrene derivatives. Substitution of one, two, or three methyl groups at 6, 7, 8, or 12 in benz[a] anthracene markedly increases activity [41]. Studies of N-mustard derivatives of anthracenes and benz[a] anthracenes [42] emphasise the parallelism between carcinogenic and carcino-static properties of poly-nuclear derivatives [43]. The marked influence of a small change in chemical structure is illustrated by the sequence of anti-tumour activities lO-ethyl-9-anthryl > 9-anthryl lO-methyl-9-anthryl for the change of meso substituent from Et to H to Me [42]. 

Fig. 1. Numbering system and nomenclature for the gibberellins and their precursors (Fig. from Phinney and Spray ). ent-Kaurene is the first tetracyclic hydrocarbon in the biosynthetic pathway. GA53 is a precursor to GA] the trivial names for the gibberellins are based on the order of identification, GAj to GAj. ...

A saturated tetracyclic hydrocarbon, fra/i5-anti-/ran5-anti-rra/i5-perhydrotri-phenylene (CisH o), forms inclusion compounds not only with low molecular weight compounds, but also with polymeric molecules, such as polyethylene, polybutadiene, polyisoprene, and polyoxyethylene. 

---