10. Addition Reactions

(•••) In light of your answer to Assessment 9.47, predict the product of the following reactions we have seen previously where an alcohol is substituted for water.

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Working backward, design a synthesis of the following alcohol using two different epoxide/Grignard reagent combinations.

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Predict the product of the following epoxide addition reactions.

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Predict the product of the following epoxide addition reactions.

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(••) LOOKING BACK In Chapter 13, we learned that epoxide opening can give different products, depending on whether the reaction occurs under acidic or basic conditions. Explain why the epoxide shown opens identically under either set of conditions.

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In Chapter 13, we discuss the ring-opening reactions of epoxides, such as the one shown here. <IMAGE>

(a) Based on the bonds formed and the bonds broken, calculate ∆H° .

(••••) LOOKING BACK Chapter 8 discussed the synthesis of cholesterol, which proceeds by a cationic cyclization cascade. Without looking back, suggest a mechanism by which the following reaction occurs. [The carbons have been numbered for you.]

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Despite it being equally favorable, opening of the epoxide does not happen in the absence of an acid catalyst. How does acid make the reaction faster? Demonstrate this concept by directly comparing the reaction coordinate diagram for both situations A and B.

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(•••) The reactivity of cyclopropanes often mimics that of alkenes. (b) Besides opening the three-membered ring, what is the driving force for this reaction?

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 (••••) Suggest mechanisms for the following reactions, which are similar to the mechanism we saw for lanosterol biosynthesis at the end of Chapter 8.

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 (••••) Suggest mechanisms for the following reactions, which are similar to the mechanism we saw for lanosterol biosynthesis at the end of Chapter 8.

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Three arene oxides can be obtained from phenanthrene.

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a. Draw the structures of the three phenanthrene oxides.

Ethylene oxide reacts readily with HO- because of the strain in the three-membered ring. Explain why cyclopropane, a compound with approximately the same amount of strain, does not react with HO-.

Propose a mechanism for each of the following reactions:

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Three arene oxides can be obtained from phenanthrene.

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d. Which of the three phenanthrene oxides is most likely to be carcinogenic?

How do the major products obtained from rearrangement of the following arene oxides differ?

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What products are obtained from the reaction of cyclohexene oxide with

a. methoxide ion?

Draw all possible resonance contributors for the two carbocations in the preceding reaction. Use the resonance contributors to explain why 1-naphthol is the major product of the reaction.

The existence of the NIH shift was established by determining the major product obtained from rearrangement of the following arene oxide, in which a hydrogen has been replaced by a deuterium.

b. What would be the major product if the carbocation forms phenol by losing H+ or D+, rather than by going through the NIH shift?

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Which of the following reactions occurs more rapidly?

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What products are obtained from the reaction of cyclohexene oxide with

b. methylamine?

b. A small amount of a product containing a six-membered ring is also formed. Draw the structure of that product.

c. Why is so little six-membered ring product formed?

What stereoisomers are obtained from the reaction of the alkenes in [PROBLEM 10-32] with a peroxyacid ­followed by reaction with hydroxide ion?

What stereoisomers are obtained from the reaction of the alkenes in [PROBLEM 10-32] with a peroxyacid ­followed by reaction with hydroxide ion?

Three arene oxides can be obtained from phenanthrene.

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c. If a phenanthrene oxide can lead to the formation of more than one phenol, which phenol will be obtained in greater yield?

Cellosolve® is the trade name for 2-ethoxyethanol, a common industrial solvent. This compound is produced in chemical plants that use ethylene as their only organic feedstock. Show how you would accomplish this industrial process.

Show the rest of the mechanism for formation of the cyclized intermediate in Figure 14-6.

Predict the products of the following reactions.

(g) trans-2,3-epoxyoctane + H⁺, H₂O

(h) propylene oxide + methylamine (CH₃NH₂)

Propylene oxide is a chiral molecule. Hydrolysis of propylene oxide gives propylene glycol, another chiral molecule.

(a) Draw the enantiomers of propylene oxide.

(b) Propose a mechanism for the acid-catalyzed hydrolysis of pure (R)-propylene oxide.

Predict the major products of the following reactions, including stereochemistry.

f. trans-pent-2-ene + peroxyacetic acid in water

a. Propose a mechanism for the conversion of cis-hex-3-ene to the epoxide (3,4-­epoxyhexane) and the ring-opening reaction to give the glycol, hexane-3,4-diol. In your mechanism, pay particular attention to the stereochemistry of the intermediates and products.

b. Repeat part (a) for trans-hex-3-ene. Compare the products obtained from cis- and trans-hex-3-ene. Is this reaction sequence stereospecific?

Predict the major product when each reagent reacts with ethylene oxide.

(d) PhNH2 (aniline)

(e) KCN (potassium cyanide)

(f) NaN3 (sodium azide)

The following reaction resembles the acid-catalyzed cyclization of squalene oxide. Propose a mechanism for this reaction.

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Predict the major products of the following reactions, including stereochemistry where appropriate.

(c) (2S,3R)-2-ethyl-2,3-dimethyloxirane + CH3O- / CH3OH

(d) (2S,3R)-2-ethyl-2,3-dimethyloxirane + H+ / CH3OH

Under the right conditions, the following acid-catalyzed double cyclization proceeds in remarkably good yields. Propose a mechanism. Does this reaction resemble a biological process you have seen? 

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There are two mechanisms by which each of the two enantiomers can form in the reaction shown in Figure 9.37. Show them.

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Show an arrow-pushing mechanism for reactions 1–4 in Figure 9.37.

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Limonene is one of the compounds that give lemons their tangy odor. Show the structures of the products expected when limonene reacts with an excess of each of these reagents. <IMAGE>

f. peroxyacetic acid in acidic water