text:  Research involving the reaction was relatively quiet in subsequent years , until in the mid @-@ 1980s when several syntheses employing the <unk> <unk> were published . Shown below are key steps in the syntheses of <unk> and Nor @-@ <unk> , the latter of which is thought to proceed via an unusual <unk> @-@ <unk> isomerization that generates the <unk> ketone . 
  