Reduction of Strained Polycycles:  How Much Strain Can a Pyrene Anion Take?

The reduction of a series of [n](2,7)pyrenophanes (n = 7-10) with lithium or potassium metal shows that the strain in the system, controlled by the length of the tether, determines the nature of the reduction products. The reduction of [7](2,7)pyrenophane (2) and [2]metacyclo[2](2,7)pyrenophane (3) leads to reductive dimerization followed by novel intramolecular sigma-bond formation as a means of escaping strained anti-aromaticity. [8](2,7)Pyrenophane (4) affords only reductive dimerization, and no two-electron reduction is observed. The reduction of [9](2,7) pyrenophane (5) and [10](2,7)pyrenophane (6) leads to reductive dimerization, followed by the formation of a dianionic anti-aromatic species, which eventually cleaves the solvent, THF-d(8). The similarity between the reduction of the latter systems and the reduction of pyrene (1) is discussed.