Multistep synthesis problem

When you see a synthesis problem for the first time, you are not expected to immediately know the answer. I cannot stress this enough. It is so common for students to get overly anxious when they see synthesis problems that they cannot solve. Get used to it. This is the way it is supposed to be. Going back to our chess analogy, you don t need to make a move as soon as it is your turn. You are allowed to think about it first. In fact, you are supposed to think about it first. So, how do you begin thinking about a multistep synthesis problem where you do not immediately see the solution The most powerful technique is called retro synthetic analysis. This means that you analyze the problem backward. Let s see how this works with an example ... 

The synthesis problem above is a multistep synthesis problem, because we do not have a single reaction that allows us to do this transformation in just one step. So the best way to start is to first look at the product and work our way backward. 

If you don t know your reactions, you can t possibly solve a multistep synthesis problem. Knowing the reactions includes the reactants, products, conditions, regiochemistry, and stereochemistry. Flashcards are a useful means of learning the reactions. On the front side of the card, write the reactants and conditions, and on the reverse side, write the products, regiochemistry, and stereochemistry. Learn the cards in one direction first (identifying what s on the back based on what you see on the front), and then learn them in reverse (knowing what s on the front when you look at the back). You must know the reactions backwards and forwards. (Shuffle the deck often.)... 

Many times, multistep synthesis problems start with an alkane. An efficient way of adding a functional group to that alkane is to brominate (or chlorinate) the alkane through a free-radical reaction. 

Retrosynthetic analysis is a method for tackling synthesis problems, especially multistep synthesis problems. The application of this technique involves working the problem backwards, starting at the final product and ending up with the initial reactants. 

When applying retrosynthetic analysis to a multistep synthesis problem, you must work backwards. If you become lost, as a last resort you may want to look at the forward reactions. However, the forward process often goes off on a tangent or leads to a cul-de-sac. 

After finishing a multistep synthesis problem, spend some time working on another problem or task. Then come back and check each step in both the forward and the reverse direction. You should pay particular attention to both the regiochemistry and the stereochemistry of each step. In addition, if one of the steps involves a molecule with more than one functional group, make sure the reaction only alters the desired functional group. 

Q Use retrosynthetic analysis to solve multistep synthesis problems with alkenes as reagents, intermediates, or products. 

Multistep synthesis problems are useful for exercising your knowledge of organic reactions, and in Chapter 8 we illustrated a systematic approach to synthesis. Now we apply this approach to a fairly difficult problem emphasizing alkyne chemistry. The compound to be synthesized is cA-2-methylhex-4-en-3-ol. (The 3-ol means there is an alcohol —OH group on C3.)... 

In this appendix, we consider how an organic chemist systematically approaches a multistep synthesis problem. As with mechanism problems, there is no reliable formula that can be used to solve all synthesis problems, yet students need guidance in how they should begin. 

Acid Derivatives 14.2 How to Approach Multistep Synthesis Problems... 

Updated End-of-Chapter Problems There are plentiful end-of-chapter problems, with the majority categorized by topic. A red problem number indicates an applied, real-world problem. There are numerous multistep synthesis problems, many dealing with the synthesis of important pharmaceuticals, and Reactions in Context problems dealing with functional group transformations of more complex molecules. 

In the previous few chapters, we developed several synthesis strategies that enable us to move the location of a functional group or change its identity. Let s briefly review these techniques, as they will be extremely helpful when solving multistep synthesis problems. 

If you felt comfortable with those problems, then you should be ready to move on to solving some multistep synthesis problems. Let s see an example ... 

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