Ch. 13 - Alcohols, Ethers and Related Compounds: Substitution and Elimination

Mullins - Organic Chemistry: A Learner Centered Approach 1st Edition

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Mullins 1st Edition

Ch. 13 - Alcohols, Ethers and Related Compounds: Substitution and Elimination

Problem 84a

Chapter 12, Problem 84a

Show how a protecting group might be used to make these reactions successful.
(a)

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Identify the functional groups in the starting material: The molecule contains a hydroxyl group (OH) and a chloro group (Cl) attached to a benzene ring. The target molecule has an alkyne group instead of the chloro group.

Recognize the need for a protecting group: The hydroxyl group is susceptible to reactions that might interfere with the transformation of the chloro group to an alkyne. Protecting the hydroxyl group will prevent unwanted side reactions.

Select an appropriate protecting group: A common protecting group for alcohols is the silyl ether, such as tert-butyldimethylsilyl (TBS) ether. This group can be introduced using a silyl chloride reagent in the presence of a base.

Perform the protection step: React the starting material with TBS-Cl and a base like imidazole to convert the hydroxyl group into a TBS ether, thus protecting it from further reactions.

Carry out the desired transformation: With the hydroxyl group protected, proceed with the conversion of the chloro group to an alkyne. This can be achieved through a series of reactions, such as elimination to form an alkene followed by a Sonogashira coupling to introduce the alkyne group.

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Key Concepts

Here are the essential concepts you must grasp in order to answer the question correctly.

Protecting Groups

Protecting groups are chemical moieties that temporarily mask reactive functional groups in a molecule, allowing for selective reactions to occur without interference. They are crucial in multi-step organic synthesis, as they enable chemists to control the reactivity of specific sites, ensuring that desired transformations can be achieved without unwanted side reactions.

Functional Group Reactivity

Different functional groups exhibit varying reactivities under specific conditions. Understanding the reactivity of functional groups is essential for designing synthetic pathways, as it helps predict how a molecule will behave in a reaction. By using protecting groups, chemists can manipulate these reactivities to achieve desired outcomes in complex organic transformations.

Deprotection

Deprotection is the process of removing a protecting group after the desired reaction has taken place. This step is critical in restoring the original functional group for further reactions or for the final product. The choice of protecting group often depends on the conditions required for deprotection, which must be compatible with the other functional groups present in the molecule.

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Related Practice

Textbook Question

Using IUPAC rules, name the following molecules.

(b)

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Textbook Question

A variety of organometallics, which as strong nucleophiles can react with epoxides, are introduced in Chapter 16. Predict the product of these reactions. [Hint: Assume the carbon–metal bond in each is ionic, with the carbon possessing the negative charge.]

(b)

(c)

Show how a protecting group might be used to make these reactions successful.

(b)

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