Dianions of 1,4-Bis(methylene)cyclohexane. Conformational Effects in Cyclic and Acyclic Dilithiated Hydrocarbons

Article abstract of DOI:10.1021/jo00003a010

Dimetalation of 1,4-bis(methylene)cyclohexane results in formation of the p-xylene dianion via the linearly conjugated dianion 4.In contrast, 2-methyl-1,5-hexadiene, an acyclic analogue of 1,4-bis(methylene)cyclohexane, undergoes isomerization via the linearly conjugated dianion 12, rather than hydride elimination.MNDO calculations of the conformation of dilithiated 4 and 12 show that 4 is effectively planar, with a symmetrical distribution of charge.Dilithiated 12 is nonplanar, with an almost right angle bend in the ?-system.The dianion can therefore be considered as two allyl anions which are orthogonal to each other.The difference in calculated conformations of 4 and 12 is advanced as the reason for the different reactivity of the two systems.