Question 1

Which of the following best describes the key transformation in the synthesis of semibullvalene as shown in the provided scheme?

Accepted Answer

An electrocyclic ring closure followed by a Diels-Alder reaction

Question 2

In the synthesis of estrone (Vollhardt), what is the role of $\mathrm{CeCl_3}$ in the initial step?

Accepted Answer

It acts as a Lewis acid to activate the carbonyl for nucleophilic attack.

Question 3

Which reaction in the semibullvalene synthesis involves a photochemical process?

Accepted Answer

The conversion of the bicyclic intermediate to the tricyclic product

Question 4

What is the significance of the use of $\mathrm{AgBF_4}$ in the final step of the semibullvalene synthesis?

Accepted Answer

It acts as a Lewis acid to promote cyclopropanation.

Question 5

In the estrone synthesis, why is $\mathrm{CF_3CO_2H}$ used after the silyl enol ether formation?

Accepted Answer

To remove the silyl protecting group and reveal the ketone

Question 6

Which of the following best explains the formation of two diastereomers in the steroid synthesis shown?

Accepted Answer

The stereochemistry of the Diels-Alder reaction

Question 7

What is the main driving force for the fragmentation of the azide intermediate in the semibullvalene synthesis?

Accepted Answer

Release of nitrogen gas ($\mathrm{N_2}$)

Question 8

In the context of the estrone synthesis, what is the purpose of using $\mathrm{PrOCO_2H}$ (propionic acid) in the sequence?

Accepted Answer

To promote selective hydrolysis of the silyl group

Question 9

Which of the following statements about the photochemical step in the semibullvalene synthesis is correct?

Accepted Answer

It is a [2+2] cycloaddition that requires UV light.

Question 10

In the estrone synthesis, what is the likely outcome if the silyl enol ether is not properly hydrolyzed before the final oxidation?

Accepted Answer

The oxidation will not occur efficiently, leading to a mixture of products.

Question 11

Which mechanistic feature is common to both the semibullvalene and estrone syntheses as shown?

Accepted Answer

Both involve a Diels-Alder cycloaddition.

Question 12

What is the main reason for the high selectivity (90%:10%) in the formation of estrone regioisomers in the final step?

Accepted Answer

The directing effect of the silyl group

Question 13

In the semibullvalene synthesis, which intermediate is most likely to react with $\mathrm{O_2}$ to form a hydroxyazide?

Accepted Answer

The azide intermediate after fragmentation

Question 14

Which of the following best describes the role of the Diels-Alder reaction in the estrone synthesis?

Accepted Answer

It constructs the steroid core by forming two new rings.

Question 15

What is the expected product when the azide intermediate in the semibullvalene synthesis is treated with $\mathrm{KOH}$?

Accepted Answer

A nitrogen-containing bicyclic compound

Advanced Organic Synthesis: Semibullvalene and Estrone Pathways

Study Guide - Practice Questions