Cyclization of diphenylacetylene on methylchromium σ-complexes III. Hydrogen transfer reactions

The reaction of diphenylacetylene with methylchromium systems yields cis- and trans-stilbene, cis- and trans-α-methylstilbene, α-benzylstyrene and bibenzyl as well as cyclic and linear condensation products. Studies with a specifically deuterated methylchromium system and diphenylacetylene and also experiments with deuterium oxide have established that the methyl group is the chief source of hydrogen in the formation of these products. Secondary hydrogen sources are also indicated. Transient carbene-chromium complexes are probable intermediates.