Cyclization of diphenylacetylene on methylchromium σ-complexes II. Cyclic and linear condensations

The reactions of diphenylacetylene with methylchromium systems lead to the formation of condensation products, of which the following have been isolated and identified: cis,cis-1,2,3,4-tetraphenyl-1,3-butadiene; hexaphenylbenzene; 1,2,3-triphenylnaphthalene: 1-methyl-2,3,4-triphenylnaphthalene: 1,2,3,4-tetraphenyl-1,3-cyclopentadiene and 1,2,4,5-tetraphenylbenzene. It is evident that methyl groups of the chromium complex participate in these cyclic condensations via insertions of methylene (carbene) groups into the ring skeleton. These processes are also accompanied by hydrogen-transfer reactions.