Fascinating problems in organic reaction mechanisms-VI : bromonitrocamphane anhydrobromonitrocamphane rearrangement

Abstract

The fascinating bromonitrocamphane(1)→anhydrobromonitrocamphane(2) change has been examined in detail. The structure of 2 has been confirmed by X-ray analysis and other physical data. The 1 → 2 transformation belongs to the rather uncommon fragmentation-rearrangement-recombination pathway and the three distinct stages involved, namely, the loss of the nitro group, the rearrangement of the bornane cation so generated to 4-bromocamphene(3) and the subsequent reacceptance of elements of the lost nitro group, have been confirmed on basis of experimental data, particularly employing ¹⁵N sodium nitrite. The remarkable bromonitrocamphane(1) → 4-bromotricyclene acid(8) change, the useful camphene→ 9 transformation and the amusing 15 → 16 change have been discovered. The concerted nature of the camphene → 11 reaction has been established with optically active camphene and this study has helped in identifying the stage where optical activity is lost in the 1→2 change. Kinetic studies have shown that in the highly strained tricyclic isoxazolines 11, 2 and 16, the 4-substituents, through inductive effect, greatly affect the stability of the isoxazoline ring. The facile rupture of such isoxazolines have provided an efficient route to doubly functionalized bornanes.