Synthesis one-step

It can only take three or fonr steps before the problem can get quite difficult. If you convert the sequence above into a synthesis problem, it would look like this  

If you are having tronble with synthesis problems when you first encounter them, the worst thing you can do is to give up and say Oh, well. I m not good at synthesis problems. As the conrse moves on, this attitnde will slowly kill your grade in the course. To see why this is so, let s compare organic chemistry to a game of chess. 

There are a few techniques that will make you feel more comfortable with synthesis problems, and there are exercises that you can go through to increase your proficiency in doing synthesis problems. That s what this chapter is aU about. 

As we mentioned earlier, one-step syntheses are the first synthesis problems you will encounter. They will never be more difficult than predicting products. Before you can move on to multistep syntheses, you first need to feel comfortable with one-step syntheses. 

To do this, we need to make a list of reactions, but we will leave out the reagents, so that we can repeatedly photocopy the hst and get practice filling in the reagents. 

To do this, we need to make a list, very similar to the one we made in the previous chapter on predicting products. In the list we made last chapter, we left out the products, so that we could repeatedly photocopy the list and fill in the products. This time, we will make a fist of the same reactions, but we will leave out the reagents, so that we can repeatedly photocopy the list and get practice filling in the reagents. 

As you learn more and more reactions, this list will grow. With every five new reactions, you should photocopy all of the reactions that you have recorded here. Then, start filling in the reagents on the photocopy. If you cannot fill them all in, go back to the previous chapter where you recorded the reactions. Repeat this procedure whenever you have entered five new reactions. 

For now, skip forward a few pages. We have some techniques to go over that will help you solve synthesis problems. 

Remember not to fill in the reagents or the mechanisms. For each reaction, just draw the starting material in front of the arrow and the products after the arrow. Leave the space above the arrow empty. You will fill in the reagents when you photocopy these pages  

If necessary, review the suggested sections to prepare for this chapter. 

PLUS Visit www.wileyplus.com to check your understanding and for valuable practice. 

The most straightforward synthesis problems are the ones that can be solved in just one step. For example, consider the following  

1 Identify the reagents necessary to accomplish each of the transformations shown below. If you are having trouble, the reagents for these transformations appear on page 444, but you should first try to identify the reagents yourself without help  

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You must make sure that you have this reaction at your hngertips, since it will appear several times thronghont the rest of yonr organic chemistry conrse. Let s practice a bit. We will begin with a few problems that are just one-step syntheses (Grignard) to make snre yon got it. Then, the last two problems in this problem set will be multi-step syntheses (using a Grignard reaction and other reactions we have seen). 

We see that the product is a dibromide. So we ask ourselves Do we know any way of making a dibromide You can see that to answer this question, you must have first mastered one-step syntheses. If you have not yet done this for all of the reactions that you have learned so far, you will need to go back to the beginning of this chapter and do that first (if you are a student in this situation, continue reading for now, so you can see where this is all going). 

Finally, pure organocopper compounds have found applications in one-step syntheses of tri- and diorganotin halides. Its has now become well established that treatment of Grignard and organolithium reagents with tin(IV) halides always gives a mixture of products (Eqn. 1 in Scheme 1.14) rather than the desired tri- or diorganotin halides. 

Other one-step syntheses involving aromatic nucleophilic radiofluorination... 

In addition, these fused-ring systems allow a one-step syntheses of mixed arene-dienyl complexes (136) ... 

Both the acid-catalysed and the base-promoted one-step syntheses provide the most powerful procedures to obtain symmetrically substituted calixarenes having only one type of phenolic unit in the cyclic array. 

There are no one-step syntheses of A(-alkylaziridines direct from alkenes of proven generality, the most thoroughly investigated being the reactions of iV-halo- and iV,iV-dihalo-alkylamines with alkenes referred to earlier (Scheme 6). They are probably radical reactions and are not stereospecific the A(-haloamine reagents are difficult to prepare cleanly, and are rather dangerous. Representative examples (6 of 17) prepared from halogenated alkylamines are listed in Scheme 14. 

Zou, Y, Lobera, M. and Snider, B.B. (2005) Synthesis of 2,3-dihydro-3-hydroxy-2-hydroxylalkylbenzofurans from epoxy aldehydes. One-step syntheses of brosima-cutin G, vaginidiol, vaginol, smyrmdiol, xanthoarnol, and avicenol A. Biomimetic syntheses of angelicin and psoralen.. Org. Chem., 70,1761-70. 

There are relatively few examples of one-step syntheses of purines from acyclic precursors and most of them in any case probably involve intermediate imidazoles or pyrimidines... 

There are three one-step syntheses from ketones and organometallic compounds. 

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