ABSTRACT Dimetalation of limonene at room temperature occurs via loss of the two most acidic protons. This dianion is calculated to be one of the most stable possible from limonene by AM1 calculations. Metalation at reflux gives a linearly conjugated dianion which is identical to that formed by dimetation of α-terpinolene. Upon further reaction, hydrde is lost from the dianion to given a benzylic anion. Comparison of the structures from MNDO calculations of this linearly conjugated dilithiated species with that from dilithiation of 1,4-bismethylene-cyclohexane reveals that hydride elimination occurs when a C-H bond is perpendicular to the planar pi system and that at least four planar carbons are necessary for hydride loss. This is one of the few examples in the literature in which the geometry of hydride loss can be assessed.
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