University11 min

Multi-step synthesis and retrosynthesis

Work back from a target to its precursors by disconnections, order the steps, protect what needs protecting and put a number on the overall yield.

The essentials

1

Retrosynthesis, synthon, synthetic equivalent

The reasoning runs from the target back to the precursors. A disconnection, shown by the arrow ⇒\Rightarrow, mentally breaks a bond and reveals two synthons, idealised fragments. Each synthon has a synthetic equivalent, a real reagent: the acylium synthon CHX3COX+\ce{CH3CO+} has acetic anhydride (CHX3CO)X2O\ce{(CH3CO)2O} or acetyl chloride CHX3COCl\ce{CH3COCl} as its equivalent.
2

Where to disconnect

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3

Protecting groups

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4

Overall yield and convergence

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5

Atom economy

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