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Concept
Synthon
Summary
In retrosynthetic analysis, a synthon is a hypothetical unit within a target molecule that represents a potential starting reagent in the retroactive synthesis of that target molecule. The term was coined in 1967 by E. J. Corey. He noted in 1988 that the "word synthon has now come to be used to mean synthetic building block rather than retrosynthetic fragmentation structures".
It was noted in 1998 that the phrase did not feature very prominently in Corey's 1981 book The Logic of Chemical Synthesis, as it was not included in the index. Because synthons are charged, when placed into a synthesis an uncharged form is found commercially instead of forming and using the potentially very unstable charged synthons.
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 by themselves; synthetic equivalents corresponding to the synthons are reacted to produce the desired reactant. 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:
where Ph stands for phenyl.
C2 synthons - acetylene, acetaldehyde
C2H4OH synthon - ethylene oxide
carbocation synthons - alkyl halides
carbanion synthons - Grignard reagents, organolithiums, substituted acetylides
This term is also used in the field of gene synthesis—for example "40-base synthetic oligonucleotides are built into 500- to 800-bp synthons".
In 1967, E. J. Corey introduced the concept of a synthon in retrosynthetic analysis. Planning the steps of a complex molecule synthesis requires recognizing key synthons and identifying how they can be assembled into a desired product. In many retrosynthetic bond disconnections, the bond is broken heterolytically instead of homolytically, generating a carbocationtic and a carbanionic synthon.
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Ontological neighbourhood
Related publications (8)
Related concepts (2)
Grignard reagent
A Grignard reagent or Grignard compound is a chemical compound with the general formula , where X is a halogen and R is an organic group, normally an alkyl or aryl. Two typical examples are methylmagnesium chloride and phenylmagnesium bromide . They are a subclass of the organomagnesium compounds. Grignard compounds are popular reagents in organic synthesis for creating new carbon-carbon bonds. For example, when reacted with another halogenated compound in the presence of a suitable catalyst, they typically yield and the magnesium halide as a byproduct; and the latter is insoluble in the solvents normally used.
Carbanion
In organic chemistry, a carbanion is an anion in which carbon is negatively charged. Formally, a carbanion is the conjugate base of a carbon acid: where B stands for the base. The carbanions formed from deprotonation of alkanes (at an sp3 carbon), alkenes (at an sp2 carbon), arenes (at an sp2 carbon), and alkynes (at an sp carbon) are known as alkyl, alkenyl (vinyl), aryl, and alkynyl (acetylide) anions, respectively.