Diels−Alder Topochemistry via Charge-Transfer Crystals:  Novel (Thermal) Single-Crystal-to-Single-Crystal Transformations

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American Chemical Society

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Journal of the American Chemical Society

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The solid-state [4+2] cycloaddition of anthracene to bis(N-ethylimino)-1,4-dithiin occurs via a unique single-phase topochemical reaction in the intermolecular (1:1) charge-transfer crystal. The thermal heteromolecular solid-state condensation involves the entire crystal, and this rare crystalline event follows topochemical control during the entire cycloaddition. As a result, a new crystalline modification of the Diels−Alder product is formed with a crystal-packing similar to that of the starting charge-transfer crystal but very different from that of the (thermodynamically favored) product modification obtained from solution-phase crystallization. Such a single-phase transformation is readily monitored by X-ray crystallography at various conversion stages, and the temporal changes in crystallographic parameters are correlated with temperature-dependent (solid-state) kinetic data that are obtained by 1H NMR spectroscopy at various reaction times. Thus, an acceleration of the solid-state reaction over time is found which results from a progressive lowering of the activation barrier for cycloaddition in a single crystal as it slowly and homogeneously converts from the reactant to the product lattice.


Accepted version. Journal of the American Chemical Society, Vol. 123, No. 1 (2001): 87-95. DOI. © 2001 American Chemical Society, Used with permission.

Sergey V. Lindeman was affiliated with the University of Houston at the time of publication.