Synthesis of several halobisnoradamantane derivatives and their reactivity through the S(RN)1 mechanism.
Several bridgehead halobisnoradamantane derivatives (5, 7, 10, and 17) were synthesized from tricyclic diester 1 in good yields using standard methods. The reactivity through the S(RN)1 mechanism of the above compounds and the known halobisethano derivatives 24 and 25a-c was studied. Iodo derivatives 7, 10, and 25a reacted with diphenylphosphide ions in DMSO under irradiation to give the corresponding substitution and reduction products by the S(RN)1 mechanism, while iodo ketone 17 gave a mixture of the rearranged substitution product 36 and the reduction product 18. Formation of 36 takes place through a 1,5-hydrogen migration of the initially formed radical, a kind of process that has been observed for the first time in the S(RN)1 propagation steps. The diiodo derivative 24 reacted with diphenylphosphide ions under similar reaction conditions to give the substitution and/or reduction products 32, 31, 27, 25a, and 26. The intramolecular ET reaction in the monosubstitution radical anion 32*(-) seems to be faster than the intermolecular ET to the substrate, and the monoiodo derivative 25a is a reaction intermediate.