Reduction of strained polycycles: how much strain can a pyrene anion take?

The reduction of a series of npyrenophanes (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 7pyrenophane (2) and [2]metacyclo2pyrenophane (3) leads to reductive dimerization followed by novel intramolecular sigma-bond formation as a means of escaping strained anti-aromaticity. 8Pyrenophane (4) affords only reductive dimerization, and no two-electron reduction is observed. The reduction of 9 pyrenophane (5) and 10pyrenophane (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.