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Multistep Organic Synthesis: Reaction Roadmaps

Learn to plan transformations backward from the target molecule and verify each step.

Step-by-step lessonsCurated examplesInteractive practicePrintable worksheets

1. Understand the concept

Multistep synthesis combines reactions into a sequence. The key skill is to map functional-group changes and choose reagents that work with the starting material and intermediates.

Learning goal: Learn to plan transformations backward from the target molecule and verify each step.

2. Use a reliable prediction strategy

  1. Compare the target and starting material: carbon skeleton, functional groups, and stereochemistry.
  2. Work backward one transformation at a time (retrosynthesis).
  3. Choose forward reagents using known selectivity and compatibility.
  4. Check whether each proposed intermediate is accessible and whether a competing pathway dominates.

3. Follow the reaction roadmap

Three verified reaction transformations with substrates, reagents and labeled products for Synthesis Roadmaps
Illustrative pathways; reagent choice and selectivity matter. Structures are shown in condensed notation.

4. Work through examples

Worked example 1

Primary alkyl bromide to aldehyde

CH₃CH₂CH₂Br →(aq. NaOH) CH₃CH₂CH₂OH →(PCC) CH₃CH₂CHO

First substitute bromide with hydroxide by SN2, then oxidize the primary alcohol under mild conditions.

Worked example 2

Continue aldehyde to acid

CH₃CH₂CHO →(CrO₃/H₂SO₄/H₂O) CH₃CH₂CO₂H

Further oxidation converts the aldehyde into propanoic acid. Avoid choosing a reagent that would oxidize the intermediate too early.

5. Common mistakes

  • Ignoring rearrangements or E2/SN2 competition while planning.
  • Choosing harsh aqueous oxidizing conditions when an aldehyde is the target.
  • Changing the carbon count unintentionally during a functional-group interconversion.

6. Check understanding

Write a two-step conversion of 1-bromopropane to propanal.

1-Bromopropane + aqueous NaOH → 1-propanol; then PCC in anhydrous solvent → propanal.

Why should Jones oxidation not be used for the second step when propanal is the target?

Aqueous Cr(VI) oxidation generally oxidizes primary alcohols beyond the aldehyde to the corresponding carboxylic acid.

7. Practice the reactions

Use the quiz below to apply the rules to new substrates and reagents. A correct answer is explained, not merely marked.

INTERACTIVE PRACTICE

Try the reaction challenge

Answer eight curated questions. Review the explanation after each answer.

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