Chapter 10.8, Problem 8E

(a)

Interpretation Introduction

Interpretation: The structure of the major product formed from alkene indicated should be predicted.

  

Concept introduction: Hydroboration-oxidation involves the sequence of two reactions. The hydroboration stage involves the treatment of alkene with diborane that generates alkyl borane. In second stage hydrogen peroxide in alkaline medium is used to oxidize the alkyl borane produced in step 1 that leads to the synthesis of alcohols from alkenes.

Hydroboration is essentially the addition of ${\text{H}}^{-}$ and ${\text{BH}}_2$ across the alkene. For example, the reaction between ${\text{BH}}_3$ and alkene to form syn-products illustrated as follows:

  

The mechanistic pathway can be illustrated as follows:

  

In the first step one equivalent of ${\text{BH}}_{\text{3}}$ is added across the $\text{C}-\text{C π}$ bond. This addition takes place such that boron approaches to less substituted carbon while the hydride ion adds to more substituted carbon. This occurs via a four-membered transition state that leads to syn-addition. So it is apt to refer this reaction as an addition that involves overall syn addition of ${\text{BH}}_{\text{3}}$ .

Explanation of Solution

The hydroboration-oxidation productis illustrated as below.

  

Anti-Markovnikov’s Rule serves as the basis of hydroboration. It states that the negative part of reagent must go to the carbon that has fewer alkyl substituents or more $\text{H}$ atoms. Since carbon 1 is less substituted thus $\text{OH}$ must add to this carbon while $\text{H}$ to other olefin carbon in accordance with anti-Markovnikov’s Rule.

(b)

Interpretation Introduction

Interpretation: The structure of the major product formed from alkene indicated should be predicted.

  

Concept introduction: Hydroboration-oxidation involves a sequence of two reactions. The hydroboration stage involves the treatment of alkene with diborane that generates alkyl borane. In second stage hydrogen peroxide in alkaline medium is used to oxidize the alkyl borane produced in step 1 that leads to the synthesis of alcohols from alkenes.

Hydroboration is essentially the addition of ${\text{H}}^{-}$ and ${\text{BH}}_2$ across the alkene. For example, the reaction between ${\text{BH}}_3$ and alkene to form syn-products illustrated as follows:

  

The mechanistic pathway can be illustrated as follows:

  

In the first step one equivalent of ${\text{BH}}_{\text{3}}$ is added across the $\text{C}-\text{C π}$ bond. This addition takes place such that boron approaches to less substituted carbon while the hydride ion adds to more substituted carbon. This occurs via a four-membered transition state that leads to syn-addition. So it is apt to refer this reaction as an addition that involves overall syn addition of ${\text{BH}}_{\text{3}}$ .

Explanation of Solution

The hydroboration-oxidation product is illustrated as below.

  

Anti-Markovnikov’s Rule serves as a basis of hydroboration. It states that the negative part of reagent must go to the carbon that has fewer alkyl substituents or more $\text{H}$ atoms. Sincethe exo side will suffer from steric repulsion due to methyl groups so $\text{OH}$ must add to the endo side in accordance with anti-Markovnikov’s Rule.

(c)

Interpretation Introduction

Interpretation: The structure of the major product formed from alkene indicated should be predicted.

  

Concept introduction: Hydroboration-oxidation involves a sequence of two reactions. The hydroboration stage involves the treatment of alkene with diborane that generates alkyl borane. In second stage hydrogen peroxide in alkaline medium is used to oxidize the alkyl borane produced in step 1 that leads to the synthesis of alcohols from alkenes.

Hydroboration is essentially the addition of ${\text{H}}^{-}$ and ${\text{BH}}_2$ across the alkene. For example, the reaction between ${\text{BH}}_3$ and alkene to form syn-products illustrated as follows:

  

The mechanistic pathway can be illustrated as follows:

  

In the first step one equivalent of ${\text{BH}}_{\text{3}}$ is added across the $\text{C}-\text{C π}$ bond. This addition takes place such that boron approaches to less substituted carbon while the hydride ion adds to more substituted carbon. This occurs via a four-membered transition state that leads to syn-addition. So it is apt to refer this reaction as an addition that involves overall syn addition of ${\text{BH}}_{\text{3}}$ .

Explanation of Solution

The hydroboration-oxidation product is illustrated as below.

  

Anti-Markovnikov’s Rule serves as the basis of hydroboration. It states that the negative part of reagent must go to the carbon that has less alkyl substituents or more $\text{H}$ atoms.

Since the terminal olefinic carbon is less substituted $\text{OH}$ must add to it in accordance with anti-Markovnikov’s Rule.

(d)

Interpretation Introduction

Interpretation: The structure of the major product formed from alkene indicated should be predicted.

  

Concept introduction: Hydroboration-oxidation involves a sequence of two reactions. The hydroboration stage involves the treatment of alkene with diborane that generates alkyl borane. In second stage hydrogen peroxide in alkaline medium is used to oxidize the alkyl borane produced in step 1 that leads to the synthesis of alcohols from alkenes.

Hydroboration is essentially the addition of ${\text{H}}^{-}$ and ${\text{BH}}_2$ across the alkene. For example, the reaction between ${\text{BH}}_3$ and alkene to form syn-products illustrated as follows:

  

The mechanistic pathway can be illustrated as follows:

  

In the first step one equivalent of ${\text{BH}}_{\text{3}}$ is added across the $\text{C}-\text{C π}$ bond. This addition takes place such that boron approaches to less substituted carbon while the hydride ion adds to more substituted carbon. This occurs via a four-membered transition state that leads to syn-addition. So it is apt to refer this reaction as an addition that involves overall syn addition of ${\text{BH}}_{\text{3}}$ .

Explanation of Solution

The hydroboration-oxidation product is illustrated as below.

  

Anti-Markovnikov’s Rule serves as the basis of hydroboration. It states that the negative part of reagent must go to the carbon that has less alkyl substituents or more $\text{H}$ atoms. Sincehydroboration reaction gives stereospecifically syn products so $\text{OH}$ must add to carbon indicated in accordance with anti-Markovnikov’s Rule.

(e)

Interpretation Introduction

Interpretation: The structure of the major product formed from alkene indicated should be predicted.

  

Concept introduction: Hydroboration-oxidation involves a sequence of two reactions. The hydroboration stage involves the treatment of alkene with diborane that generates alkyl borane. In second stage hydrogen peroxide in alkaline medium is used to oxidize the alkyl borane produced in step 1 that leads to the synthesis of alcohols from alkenes.

Hydroboration is essentially the addition of ${\text{H}}^{-}$ and ${\text{BH}}_2$ across the alkene. For example, the reaction between ${\text{BH}}_3$ an alkene to form syn-products illustrated as follows:

  

The mechanistic pathway can be illustrated as follows:

  

In the first step one equivalent of ${\text{BH}}_{\text{3}}$ is added across the $\text{C}-\text{C π}$ bond. This addition takes place such that boron approaches to less substituted carbon while the hydride ion adds to more substituted carbon. This occurs via a four-membered transition state that leads to syn-addition. So it is apt to refer this reaction as an addition that involves overall syn addition of ${\text{BH}}_{\text{3}}$ .

Explanation of Solution

The hydroboration-oxidation product is illustrated as below.

  

Anti-Markovnikov’s rule serves as the basis of hydroboration. It states that the negative part of reagent must go to the carbon that has less alkyl substituents or more $\text{H}$ atoms. Since hydroboration reaction gives stereospecifically syn products so $\text{OH}$ must add to carbon indicated in accordance with anti-Markovnikov’s Rule.