Organic Chemistry: Concepts and Applications - Headley Allan D. 2020

Addition Reactions Involving Carbonyls and Nitriles
9.11 Applications of Addition Reactions to Synthesis

In this section, we will examine how best to make strategic choices in the use of specific reactions to accomplish transformations and the best combination of reactions if more than one reaction is required to accomplish a transformation. As pointed out in the previous chapter, an important aspect of organic chemistry is the synthesis of specific target molecules utilizing the reaction types that we have studied so far. Let us first consider the type of reactions needed to carry out the following transformation shown in Reaction (9-85).

(9-85)Image

Initial inspection of the reaction shows that the oxygen of the carbonyl functionality in the reactant has been replaced by a carbon. We have covered an addition reaction that can convert a carbonyl functionality to an alkene and that is the Wittig reaction. We have also covered a reaction that can convert an alkene into alcohols via a specific hydration reaction. Now that we have established a strategy to carry out the transformation, the next task is to select an appropriate sequence of reactions and reaction conditions to accomplish the transformation. Working backward, the last reaction needed for this transformation is shown in Reaction (9-86).

(9-86)Image

The synthesis of the alkene can be accomplished from a carbonyl compound as shown below. Note that you will have to make the appropriate selection of Wittig reagent with appropriate groups bonded to the reagent so that it gives the desired product. In this case, the carbon should be bonded to a hydrogen and a methyl group, as shown in red in Reaction (9-87).

(9-87)Image

Thus, the overall sequence of reactions needed for this transformation can be summarized as shown in Reaction (9-88). Note that the inorganic products are typically not written since we are more concerned about obtaining an organic molecule.

(9-88)Image

Problem 9.15

Show how to carry out the transformations shown below. Clearly show all reagents needed and steps in any sequence of reactions carried out. Note that these transformations are essentially the same as shown in the example, except that instead of using the ketone as a starting compound, Wittig reagents are the starting reagents.

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