Retrosynthetic arrows

Notice the retrosynthetic arrow above. That arrow indicates that we can make the desired alcohol from the ketone above, like this ... 

The process is called retrosynthetic analysis, i) => is a retrosynthetic arrow (retro = backward) that relates the target molecule to its most immediate precursors. Professor E. J. Corey originated the term retrosynthetic analysis and was the first to state its principles formerly. 

Retrosynthetic arrow (Section 11.14) An arrow used in the development of a synthetic scheme that points from the target to the reactant from which it can be prepared. 

Most of the chemistry you have learned so far has concentrated on reactions (questions like what do you need to add to X to get Y ) or on products (questions like what will happen if X and Y react together ). Now we re looking at starting materials (questions like what X and Y do you need to react together to make Z ). We re looking at reactions in reverse, and we have a special symbol for a reverse reaction called a retrosynthetic arrow (the implies arrow from logic). 

A scheme with a retrosynthetic arrow Z —. - X + Y means Z could be made from X plus Y a retrosynthetic arrow... 

This compound is used as an insect repellent, As it s an ester, we know that it can be made from alcohol plus acyl chloride, and we can represent this using a retrosynthetic arrow. 

The aromatic amide amelfolide is a cardiac antiarrhythmic agent. Because we see that it is an amide, we know that it can be made quite simply from p-nitrobenzoyl chloride and 2,6-dimethyl-aniline—again, we can represent this using a retrosynthetic arrow. Mentally breaking a molecule into its component parts like this is known as disconnection, and it s helpful to indicate the site of the disconnection with a wiggly line as we have here. 

You probably spotted immediately that daminozide is again an amide, so the best disconnection is the C-N bond, which could take us back to acyl chloride and dimethylhydrazine. This time we ve written C-N amide above the retrosynthetic arrow as a reminder of why we ve made the disconnection and we advise you to follow this practice. 

Make Cl—C5, C4—C6. Break Cl—C4. The two new a-bonds have a 1,3-relationship in a new six-membered ring, suggesting that a Diels-Alder reaction has taken place. Disconnect the Cl—C5 and C4—C6 bonds of the product to see the immediate precursor to the product, an o-xylylene. The doublebodied arrow ( ), a retrosynthetic arrow, indicates that you are working backward from the product. 

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