Question

For each of the following alcohols, which method of synthesis, (a) hydroboration?oxidation or (b) oxymercuration?reduction, can produce the alcohol relatively free of constitutional isomers and diastereomers? (Drag an alcohol to the appropriate bin if it can be made by that method.)

r each of the following alcohols, which method of synthesis, (a) hydroboration- oxidation or (b) oxymercuration-reduction, can produce the alcohol relatively free of constitutional isomers and diastereomers? (Drag an alcohol to the appropriate bin ifit can be made by that method.) (a) hydroboration-oxidation (b) oxymercuration-reductiorn ..OH OH OH CH3CH2 CH CH2CH2CH3 OH OH OH CH3CH2 CH3CH2 CH CH2CH2CH3 OH OH

Answer 1

Concepts and reason

Retrosynthesis: It’s a method of identifying the starting materials from the given target compound. In this method the target molecule was disintegrated into its respective most possible precursor.

Alkene: Its class of organic compound with functional group of carbon-carbon $\left( {{\rm{C}} = {\rm{C}}} \right)$ double bond. Alkenes are reactive due to the presence of ${\bf{\pi }}$ -bonds. Alkenes undergo addition reactions, oxidations and polymerization, and so forth.

Hydration reaction: It’s a type of addition reaction, in which water molecule is added along the double bond of the alkene to produce saturated alcoholic derivatives. In case of unsymmetrical alkene the addition reaction may result in two type of product they are explained as Markonikov product and anti Markonikov product.

Markonikov product: During the hydration of alkene the hydroxyl group was attached to the more substituted alkenic carbon and hydrogen forms bond with less substituted alkenic carbon.

Anti-Markonikov product: Its reverse of Markonikov product, in which the hydroxyl group attach to the less substituted alkenic carbon and the hydrogen was attached to the more substituted carbon alkenic carbon.

Hydroboration-oxidation: Addition of water molecule towards the alkene was done with aid of ${\rm{B}}{{\rm{H}}_{\rm{3}}}$ and ${{\rm{H}}_{\rm{2}}}{{\rm{O}}_{\rm{2}}}$ , which resulted in the formation of anti-Markonikov product

in major amount. Moreover, stereo chemically it’s a “syn-type” addition, that is ${\rm{OH}}$ and ${\rm{H}}$ were added from the same side.

Oxymercuration-reduction: In this reaction water molecule was added to alkene with the help of mercuric acetate and sodium borohydride. oxymercuration leads to the formation of Markonikov product as predominant. Stereo chemically this is “anti-type” addition reaction, in which the ${\rm{OH}}$ and ${\rm{H}}$ were added from the opposite side.

Fundamentals

Mechanism for hydroboration of alkene:

Mechanism for oxymercuration of alkene:

Given alcohols

Using retro synthetic approach the alkenes precursors were identified as shown below.

All three cyclopentane alcohol derivatives can be obtained by the hydration of methyl-cyclopentene.

Hydroboration-oxidation of the identified alkene precursors are given below

Oxymercuration-reduction for the first alkene gives the following products.

The alcohol given below cannot be prepared by either hydroboration-oxidation or oxymercuration method.

Since hex-3-ene is symmetric, hydroboration and oxymercuration of it will lead to the same alcohol derivative.

Ans:

The alcohol obtained by the hydroboration-oxidation and oxymercuration-reduction were presented in their respective bins