Ch. 8 - Alkenes I: Properties and Electrophilic Additions

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

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Mullins 1st Edition

Ch. 8 - Alkenes I: Properties and Electrophilic Additions

Problem 74c

Chapter 7, Problem 74c

In light of your answer to Assessment 8.73, predict the product of the following oxymercuration–reduction reactions, each of which results in a single product. [Don't worry about the absolute stereochemistry, though these reactions are also stereoselective.]
(c) Oxymercuration–reduction was used in the stereoselective synthesis of the macrolactone core of neopeltolide, a marine macrolide isolated from a Caribbean sponge that has potent anticancer activity (Org. Lett. 2012, 14, 2346–2349).

Verified step by step guidance

Identify the reaction type: The reaction shown is an oxymercuration-reduction, which is used to convert alkenes to alcohols without rearrangement.

Analyze the starting material: The structure provided is a complex macrolactone with an alkene group. The alkene is the site of the oxymercuration-reduction reaction.

First step - Oxymercuration: The alkene reacts with mercuric trifluoroacetate (Hg(OTFA)2) in the presence of water. This step forms a mercurinium ion intermediate, where the mercury atom is added to the less substituted carbon of the alkene, and a hydroxyl group is added to the more substituted carbon.

Second step - Reduction: Sodium borohydride (NaBH4) is used to reduce the mercurinium ion intermediate, replacing the mercury group with a hydrogen atom, resulting in the formation of an alcohol.

Predict the product: The final product will have an alcohol group at the more substituted carbon of the original alkene, maintaining the stereochemistry of the other substituents in the macrolactone core.

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Key Concepts

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

Oxymercuration-Reduction

Oxymercuration-reduction is a two-step reaction used to convert alkenes into alcohols. In the first step, an alkene reacts with mercuric acetate in the presence of water, leading to the formation of a mercurial intermediate. The second step involves the reduction of this intermediate, typically using sodium borohydride, which replaces the mercury with a hydrogen atom, yielding an alcohol. This reaction is notable for its regioselectivity and stereoselectivity.

Regioselectivity

Regioselectivity refers to the preference of a chemical reaction to yield one structural isomer over others when multiple possibilities exist. In the context of oxymercuration-reduction, the reaction typically follows Markovnikov's rule, where the more substituted carbon atom of the alkene becomes bonded to the hydroxyl group in the final alcohol product. Understanding regioselectivity is crucial for predicting the outcome of reactions involving alkenes.

Stereoselectivity

Stereoselectivity is the property of a reaction to favor the formation of one stereoisomer over others. In oxymercuration-reduction, the reaction can lead to the formation of specific stereoisomers due to the nature of the intermediate and the subsequent reduction step. Although the question specifies not to worry about absolute stereochemistry, recognizing that the reaction can produce different stereoisomers is important for understanding the overall product distribution.

Related Practice

Textbook Question

In light of your answer to Assessment 8.73, predict the product of the following oxymercuration–reduction reactions, each of which results in a single product. [Don't worry about the absolute stereochemistry, though these reactions are also stereoselective.]

(b) This reaction sequence was used in the synthesis of (+) -lineatin, a monoterpene aggregation pheromone from the female ambrosia beetle Trypodendron lineatum (Org. Lett. 2004, 6, 1449–1452).

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Textbook Question

A common situation occurs when both carbons of the mercurinium ion are secondary. In a situation like the one shown, to which carbon would you expect water to add? That is, would you expect to produce A or B? Explain your answer.

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Textbook Question

North American termite soldiers, when encountering enemy insects, contract their mandibular muscles, expelling a mixture of chemicals that essentially trap their enemies in a glue-like substance. This weapon, built into the face of the termite, is called the fontanellar gun. It releases a mixture of pinene (62%), myrcene (27%), and limonene (11%). pinene myrcene limonene 62% 27% 11%

(a) Identify the isoprene units in pinene, myrcene, and limonene.

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Textbook Question

(b) Suggest an acid-catalyzed mechanism by which pinene could be produced from limonene.

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Textbook Question

Predict the product of each of the following hydroboration–oxidation or oxymercuration–reduction reactions used in the modern synthetic organic chemistry literature (modified to use reagents we are used to seeing).

(c) A similar sequence was featured in the synthesis of muricadienin, a proposed precursor in the biosynthesis of solamin (Org. Lett. 2014, 16, 5886–5889).

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Textbook Question

The formation of five-membered ring ethers is an important goal in synthetic organic chemistry because tetrahydrofurans are contained within a number of antitumor natural products. Toward that end, a one-pot synthesis of a bis-THF containing compound was developed (Eur. J. Org. Chem. 2010, 6263–6268). Suggest a mechanism for this transformation.

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