🧠 Multi-Step Synthesis & Retrosynthetic Analysis

E. J. Corey's retrosynthetic logic: work backward from the target, applying disconnections to reveal simpler precursors and recognized synthons.

Core moves

• Disconnection — break a strategic bond; ⇒ arrow indicates "is made from".
• Synthons — idealized cation/anion fragments (acyl cation = RCO⁺, enolate = ⁻CH₂COR).
• Synthetic equivalents — real reagents that deliver a synthon (acyl chloride for RCO⁺, lithium enolate for the α-anion).
• Functional Group Interconversion (FGI) — rewrite a hard-to-disconnect FG into one that disconnects cleanly.

Strategic bonds to target first

1. Bonds α,β to a carbonyl (aldol/Michael disconnections)
2. Bonds to a ring (Diels-Alder, EAS, intramolecular aldol)
3. C–heteroatom bonds (SN2, reductive amination, Williamson)

Protecting groups — when to use and remove acetals (carbonyls), TMS/TBS ethers (alcohols), Boc/Cbz (amines), and the principle of orthogonal protection.

Convergent vs linear synthesis — convergent routes (separate fragments joined late) carry far higher overall yield than long linear sequences.