Synthon

[2] It was noted in 1998[3] that the phrase did not feature very prominently in Corey's 1981 book The Logic of Chemical Synthesis,[4] as it was not included in the index.

Carbon-carbon bonds, for example, exist ubiquitously in organic molecules, and are usually disconnected during a retrosynthetic analysis to yield carbocationic and carbanionic synthons.

oxonium and acylium ions are carbocationic synthons for carbonyl compounds such as ketones, aldehydes and carboxylic acid derivatives.

In the forward direction, the researchers used an intramolecular aldol reaction catalyzed by titanium tetrachloride to form the tetrahydrofuran ring of hops ether.

The mechanism of the reaction involves C-C pi-bond attack onto an iminium ion, usually formed in situ from the condensation of an amine and an aldehyde.