Strategy in Retrosynthesis: Strategic Bonds and Convergent Routes
A target with several rings and stereocentres offers more disconnections than anyone can evaluate one at a time. Strategy narrows the field: cut the bonds that simplify the skeleton most, and arrange the route so that fragments of similar size meet late.
What a learner can do afterwards
- Ranks candidate disconnections by how much skeletal simplification each one buys
- Rewrites a linear route as a convergent one and compares the overall yield of the two
- Uses a symmetry element in the target to cut the number of distinct steps
- Names the functional group interconversion that opens a disconnection which is otherwise blocked
1 · Read
A target with several rings offers more cuts than you can try one by one. Rank candidate disconnections by how much skeletal simplification each buys. The best cuts split rings and divide the skeleton near its middle.
You already multiply step yields to price a route, and long lines decay fast. Two steps at 0.9 each give 0.81, while five steps at 0.9 give 0.59. Build fragments of similar size and join them late, and the longest line stays short.
Use symmetry to cut the number of distinct steps: one operation can install the same feature twice. And when a cut looks blocked, try a functional group interconversion first, since swapping the group can open the disconnection.
Rewrite any linear route as a convergent one and compare the two yields. If the branches meet late and stay balanced, the convergent route almost always wins.
Cut where simplification is greatest, exploit symmetry, and join balanced fragments late.
2 · Watch
Take it off screen
Where it sits
8 questions wait behind this lesson, each with its answer explained. Every answer feeds the sky: stars light as they are learned, and dim when it is time to come back.