| Retrosynthesis |
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| CATEGORIES ABOUT RETROSYNTHETIC ANALYSIS | |
| chemical synthesis | |
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INTRODUCTION Just as Chemical Reaction s can be viewed in the ''synthetic direction'', from starting materials to products, reactions can also be viewed ''retrosynthetically'': from products to starting materials. Likewise, entire syntheses can be viewed retrosynthetically. The power of retrosynthetic analysis becomes evident in the design of a synthesis. The goal of retrosynthetic analysis is structural simplification. Often, a synthesis will have more than one possible synthetic routes. Retrosynthesis is well suited for discovering different synthetic routes and comparing them in a logical and straightfoward fashion. DEFINITIONS ;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 : An idealized molecular fragment. A synthon and the corresponding commercially available material are shown below. ;Target: The desired final compound. ;Transform: The exact reverse of a synthetic reaction; the formation of starting materials from a single product. 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 an analysis. This allows bidirectional search techniques. Transform-based Strategies The application of transformations to retrosynthetic analysis can lead to powerful reductions in molecular complexity. Unfortuantely, 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 one or more key bond disconnections may lead to the identification of key substructures or difficult to identify rearrangment transformations.
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