Orbital interactions. VIII. Competition kinetic measurements of the Birch reduction of some compounds having the bicyclo[2,2,1]heptadiene framework as a means of investigating orbital interactions through space in these systems

Abstract

Relative rate constants for the Birch reduction (Li/liq. NH₃/t-butyl alcohol) of norbornadiene (1),1,4-dihydro-1,4-methanonaphthalene (3), 9-(1-methylethylidene)-1,4-dihydro-1,4-methanonaphthalene(5), 1,4- dihydro-1,4-epoxynaphthalene (7), lithium benzoate, α-methylstyrene, and the hexahydrobenzenomethanoanthracene(20a), were obtained and compared with that obtained for the reduction of norbornene from an earlier study. Compounds (1), (3) and (5) were some 10⁵ times more readily reduced than norbornene. These results are best explained in terms of the presence of through-space interactions operating between the two lowest unoccupied molecular orbitals in these molecules. The Birch reduction of (7) gave mainly 1,4-dihydronaphthalene (17).A mechanism for this reaction is presented.