Organic chemistry.(Highlights)

Playing with ring size

Synthetic chemists like to work with six-membered rings, but admire target structures with five and seven membered rings. Cephalotaxine (5) is a good example of such a target, with its eye-catching fusion of two five-membered rings on the seven-membered ring, Li and Wang use an approach in which they employ a classic aldol cyclopentenone synthesis, but then exploit the resulting C=C double bond to rearrange the structure to produce the required skeleton. The diketone (1) is converted with base into (2), but the rearrangement conditions to form (4) are unusual. The result is ascribed (see Figure 1) to the reductive interception of an aziridinium …