Diphenylmethane, cyclization with

Interesting possibilities of synthesis arise when elimination leads to cyclic products. Such cyclization is fairly common with aromatic compounds. The mixture of products obtained from diphenylmethane contains about 25 per cent fluorene 2S> (Table 3). Similarly, benzophenone yields about 30 per cent fluorenone 20). The same method can be applied to the synthesis of heterocyclic compounds. Diphenylamine yields up to 30 per cent carbazol 26 di-phenylether about 10 per cent dibenzofurane 16). 

Phenylpropanoic, 4-phenylbutanoic and 3,3-diphenylpropanoic acids were transformed with xenon difluoride to the corresponding fluorinated products without indication of free-radical rearrangement or cyclization, while phenylacetic acid in the presence of benzene produced diphenylmethane, indicating the involvement of a trivalent species (Scheme 44). Trifluoromethylbenzene was formed in 42% yield by reaction of trifluo-roacetic acid with benzene35-37. 

Whereas Hunter did not obtain the catenane 16 directly from 14 and 17, but only after preparation of the intermediate 15, we independently succeeded in the same year in a one-step synthesis of a substituted representative of the same catenane type 16 (R = OCH3) starting from the simple components 17 and 18 [31], In connection with earlier syntheses of basket-shaped host molecules [32], we had applied the cyclohexylidene-substituted diamine 17 [33] instead of unsubstituted diphenylmethane, p-phenylene and naphthalene units in order to increase the solubility of macropolycyclic lactams of type 19. The OCH3-substituents introduced via 18 are intended to be cleaved to OH-groups after the cyclization process. This should be useful for further bridging and, in particular, for attaching the bottom of the basket (spacer in 20). 

Diphenylethane 22 is more reactive towards chlorosulfonic acid than diphenyl-methane 18, probably as a result of increased hyperconjugative electron release from the ethylene bridge bond. When diphenylethane 22 was heated with a large excess of chlorosulfonic acid (20 equivalents) at 100 °C (4 hours), the cyclized product 24 was isolated in excellent (90%) yield (Equation 8). The cyclization to the seven-membered ring sulfone 24 was more easily achieved than the analogous conversion of diphenylmethane 18 to the six-membered ring sulfone 21... 

The latter conversion provides another example of the cyclization of diaryl compounds by treatment with a very large excess of chlorosulfonic acid under reflux. Analogous cyclizations occurred with biphenyl and diphenylmethane (see Section 2, p 40). 

---