Enolate anions, arylation dianions

The functional equivalent of an enolate dianion (103) was prepared by Stork et al. by treatment of en-amine (104) with r-butyllithium. ° This anion crystallized as the symmetrical dimer (105) with the car-banionic carbon nearly symmetrically bridging two lithium atoms as shown in (105). Doubly bridging carbons represent a characteristic feature of these lithiated vinylic anions and this structural feature is normally expected in these compounds as well as in aryl anions (see ref. 11). 

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