Synthon

A synthon is a concept in retrosynthetic analysis. It is defined as a structural unit within a molecule which is related to a possible synthetic operation. The term was coined by E.J. Corey. It is noted ^[1] that the phrase does not feature very prominently in Corey's book, The Logic of Chemical Synthesis, as it is not included in the index.

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Example

In planning the synthesis of phenylacetic acid, two synthons are identified. A nucleophilic "-COOH" group, and an electrophilic "PhCH₂⁺" group. Of course, both synthons do not exist per se; synthetic equivalents corresponding to the synthons are reacted to produce the desired product. In this case, the cyanide anion is the synthetic equivalent for the ^-COOH synthon, while benzyl bromide is the synthetic equivalent for the benzyl synthon.

The synthesis of phenylacetic acid determined by retrosynthetic analysis is thus:

1. PhCH₂Br + NaCN → PhCH₂CN + NaBr
2. PhCH₂CN + 2 H2O → PhCH₂COOH + NH3

Common synthons

• C1 synthons - carbon dioxide, carbon monoxide, cyanide
• C2 synthons - acetylene, acetaldehyde
• -C₂H₄OH synthon - ethylene oxide
• carbocation synthons - alkyl halides
• carbanion synthons - Grignard reagents, organolithiums, substituted acetylides

References

1. ^ Organic Synthesis, the science behind the art. W.A. Smit, A.F. Buchkov, R.Cople, Royal Society of Chemistry ISBN 0-85404-544-9