Remarkable increases of molecular complexity in a single procedural step are achieved with the title reaction. Only a slight modification in the substitution pattern on the acyclic precursor 2 can change the mode of tetracyclization to either yield skeletons of type 1 or 3 exclusively.

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Under Palladium catalysis [Pd(OAc)2, K2CO3, LiCl, Bu4NBr, DMF] o‐bromo‐trans‐stilbene (trans‐7a) reacts to give 9,10‐dibenzylidene‐9,10‐dihydroanthracene (4a) with formation of a new six‐membered ring. The (Z) diastereomer crystallizes preferentially to give pure (Z)‐4a, as proved by X‐ray crystal structure analysis. A variety of substituted o‐bromostilbenes and heterocyclic analogs 7 were prepared by Wittig olefination of o‐bromobenzaldehyde with substituted benzyltriphenylphosphonium ylides, Wittig‐Horner‐Emmons olefination of arenecarbaldehydes with diethyl o‐bromobenzylphosphonate or Wittig olefination of substituted benzaldehydes with substituted (o‐bromobenzyl)‐diphenylphosphonium ylides, respectively. The cis‐o‐bromostilbenes were photoisomerized to the trans diastereoisomers trans‐7 by irradiation in the presence of diphenyl disulfide. All of these o‐bromo‐trans‐stilbenes trans‐7a–g and trans‐7j, k under palladium catalysis reacted to the corresponding 9,10‐bis(arylmethylene)‐9,10‐dihydroanthracenes 4, mostly as mixtures of (E) and (Z) diastereomers (50‐97 % yield). The (Z) diastereomer of the parent 4a and the alkyl‐substituted compounds 4c and 4e could be purified by simple crystallization, and in some runs, only (Z)‐4a, c, e were obtained. Among the heterocyclic analogs trans‐7h, i only the furyl derivative trans‐7h reacted (76 % yield) cleanly, whereas the pyridine analog trans‐7i gave a mixture of products from which the rather sensitive product 4i could not be isolated in pure form. The cis‐o‐bromostilbenes cis‐7a, c cyclized to phenanthrenes under the same conditions (70‐71 % yield). The UV spectra of compounds 4a, c–k are similar to that of anthracene, and so are the oxidation and reduction potentials of (Z)‐4a.

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364.[9] The C1S meso protons and other protons cannot be assigned becduse of overlap between b = 0 and 6 = 4 of the NMR spectra of 1.2, and solvent.