Retrosynthetic analysis

;Disconnection: A retrosynthetic step involving the breaking of a bond to form two (or more) synthons. ;Retron: A minimal molecular substructure that enables certain transformations. ;Retrosynthetic tree: A directed acyclic graph of several (or all) possible retrosyntheses of a single target. ;Synthon: A fragment of a compound that assists in the formation of a synthesis, derived from that target molecule. A synthon and the corresponding commercially available synthetic equivalent are shown below: ;Target: The desired final compound. ;Transform: The reverse of a synthetic reaction; the formation of starting materials from a single product. ==Example==

Shown below is a retrosynthetic analysis of phenylacetic acid: In planning the synthesis, two synthons are identified. A nucleophilic "-COOH" group, and an electrophilic "PhCH2+" group. Both synthons do not exist as written; 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: : PhCH2Br + NaCN → PhCH2CN + NaBr : PhCH2CN + 2 H2O → PhCH2COOH + NH3 In fact, phenylacetic acid has been synthesized from benzyl cyanide, itself prepared by the analogous reaction of benzyl bromide with sodium cyanide. ==Strategies==

Functional group strategies Manipulation of functional groups can lead to significant reductions in molecular complexity. Stereochemical strategies Numerous chemical targets have distinct stereochemical demands. Stereochemical transformations (such as the Claisen rearrangement and Mitsunobu reaction) can remove or transfer the desired chirality thus simplifying the target. Structure-goal strategies Directing a synthesis toward a desirable intermediate can greatly narrow the focus of analysis. This allows bidirectional search techniques. Transform-based strategies The application of transformations to retrosynthetic analysis can lead to powerful reductions in molecular complexity. Unfortunately, powerful transform-based retrons are rarely present in complex molecules, and additional synthetic steps are often needed to establish their presence. Topological strategies The identification of one or more key bond disconnections may lead to the identification of key substructures or difficult to identify rearrangement transformations in order to identify the key structures. • Disconnections that preserve ring structures are encouraged. • Disconnections that create rings larger than 7 members are discouraged. • Disconnection involves creativity. ==See also==