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Ch. 8 - Alkenes I: Properties and Electrophilic Additions
Mullins - Organic Chemistry: A Learner Centered Approach 1st Edition
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All textbooksMullins 1st EditionCh. 8 - Alkenes I: Properties and Electrophilic AdditionsProblem 75
Chapter 7, Problem 75

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.
Chemical reaction diagram illustrating the oxymercuration of alkenes to form five-membered ring ethers.

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1
The reaction begins with the addition of mercuric acetate (Hg(OAc)2) to the alkene. This step forms a mercurinium ion intermediate, which is a cyclic structure where mercury is bonded to the two carbons of the former double bond.
The mercurinium ion is attacked by the hydroxyl group on the adjacent carbon, leading to the formation of the first tetrahydrofuran ring. This step involves the nucleophilic attack of the hydroxyl group on the more substituted carbon of the mercurinium ion, opening the ring and forming an ether linkage.
The second hydroxyl group then attacks the remaining mercurinium ion, forming the second tetrahydrofuran ring. This step is similar to the first ring formation, where the hydroxyl group acts as a nucleophile and attacks the more substituted carbon, resulting in the formation of the second ether linkage.
After the formation of both tetrahydrofuran rings, sodium borohydride (NaBH4) is used to reduce the mercury from the structure. This reduction step replaces the mercury with hydrogen, completing the transformation to the bis-THF compound.
Throughout the mechanism, stereochemistry is preserved due to the nature of the cyclic intermediates and the regioselectivity of the nucleophilic attacks. The final product retains the stereochemistry of the original hydroxyl groups, resulting in the specific orientation of the tetrahydrofuran rings.

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Key Concepts

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

Five-Membered Ring Ethers

Five-membered ring ethers, such as tetrahydrofuran (THF), are cyclic compounds featuring an ether functional group. Their formation is significant in organic synthesis due to their presence in various biologically active molecules, including antitumor agents. Understanding the properties and reactivity of these compounds is essential for designing synthetic pathways that yield them efficiently.
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One-Pot Synthesis

One-pot synthesis refers to a method where multiple reaction steps are performed sequentially in a single reaction vessel without isolating intermediates. This approach enhances efficiency and reduces the time and resources needed for synthesis. In the context of forming bis-THF compounds, it allows for the simultaneous formation of multiple bonds and ring structures, streamlining the synthetic process.
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Reaction Mechanisms

A reaction mechanism is a detailed description of the step-by-step process by which reactants transform into products. It includes the identification of intermediates, transition states, and the types of chemical bonds formed or broken. Proposing a mechanism for the transformation in the question involves understanding the underlying chemistry, such as nucleophilic attacks and ring closures, which are critical for predicting the outcome of the synthesis.
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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

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).

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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

The acid-catalyzed hydration we learned here in Chapter 8 is reversible.

(a) Propose a mechanism for the formation of an alkene from an alcohol.

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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

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%).

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

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