Cycloalkadienes, reduction

Under the conditions which cause migration of the double bonds, e.g. treatment with sodium and especially potassium, the isolated double bonds can become conjugated, and thus they undergo reduction by metals. Some macrocyclic cycloalkadienes were reduced (predominently to trans cycloalkenes) by treatment with potassium on alumina in a hydrogen atmosphere [350]. 

The formation of additional products (substituted cyclohexadienes and cyclopentadienes) in some of the reactions, specifically when cyclopropenes with one or two phenyl groups in the 3-position are employed, mechanistically can be rationalized by a reaction pathway involving a nickelacyclobutene 7 with at least one 7t-coordinated alkyne that inserts into the four-mem-bered metallacycle forming a metallacyclohexadiene 8. Reductive elimination may then proceed resulting in cycloalkadienes. 

Lacombe F, Radkowski K, Seidel G. Fiirstner A. ( )-Cyclo-alkenes and ( ,E)-cycloalkadienes by ring closing diyne or enyne-yne metathesis/semi-reduction. Tetrahedron 2004 60 7315-7324. 

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