Selective opening of ring C in the morphine skeleton by an unexpected cleavage of the C5-C6 bond in cycloadducts of thebaine and acyl nitroso compounds

[GRAPHICS] Acyl nitroso cycloadducts of the alkaloid thebaine undergo an unexpected cleavage of the C5-C6 bond when treated with 2 equiv of samarium(II) iodide in THF to give novel hexahydrobenzazocine products. A proposed mechanism for the transformation involves rearrangement of the initial radical anion.