Using any necessary inorganic reagents, show how you would convert acetylene and isobutyl bromide to
(b) (±)-2,7-dimethyloctane-4,5-diol.

검증된 단계별 안내

Step 1: Begin by converting acetylene (C₂H₂) into a terminal alkyne. This can be achieved by reacting acetylene with sodium amide (NaNH₂) in liquid ammonia (NH₃) to generate the acetylide ion (C≡C⁻). Then, react the acetylide ion with methyl iodide (CH₃I) to form propyne (CH₃C≡CH).

Step 2: Perform a hydroboration-oxidation reaction on propyne to convert the terminal alkyne into an aldehyde. Use disiamylborane (Sia₂BH) for selective hydroboration, followed by oxidation with hydrogen peroxide (H₂O₂) in the presence of sodium hydroxide (NaOH). This yields propanal (CH₃CH₂CHO).

Step 3: React isobutyl bromide ((CH₃)₂CHCH₂Br) with magnesium (Mg) in dry ether to form the corresponding Grignard reagent, isobutylmagnesium bromide ((CH₃)₂CHCH₂MgBr). Then, perform a nucleophilic addition reaction between the Grignard reagent and propanal to form a secondary alcohol, 2,7-dimethylheptanol.

Step 4: Oxidize the secondary alcohol to a ketone using an oxidizing agent such as pyridinium chlorochromate (PCC). This converts 2,7-dimethylheptanol into 2,7-dimethylheptan-4-one.

Step 5: Perform a stereoselective reduction of the ketone using a reducing agent like sodium borohydride (NaBH₄) or lithium aluminum hydride (LiAlH₄) to yield (±)-2,7-dimethyloctane-4,5-diol. This reduction introduces two hydroxyl groups at the 4 and 5 positions, completing the synthesis.

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주요 개념

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Alkyne Reactivity

Acetylene is a simple alkyne that can undergo various reactions, including hydrogenation, halogenation, and nucleophilic addition. Understanding the reactivity of alkynes is crucial for predicting the products of reactions involving acetylene, especially when forming more complex molecules like alcohols or diols.

Nucleophilic Substitution

Isobutyl bromide is a primary alkyl halide that can participate in nucleophilic substitution reactions. In these reactions, a nucleophile attacks the carbon atom bonded to the bromine, leading to the replacement of the bromine atom. This concept is essential for understanding how to introduce new functional groups into organic molecules.

Stereochemistry of Alcohols

The formation of (±)-2,7-dimethyloctane-4,5-diol involves the introduction of hydroxyl groups at specific positions on the carbon chain. Understanding stereochemistry is vital, as it determines the spatial arrangement of atoms in the molecule, which can affect the compound's properties and reactivity. The term (±) indicates a racemic mixture, highlighting the importance of chirality in organic synthesis.

Using any necessary inorganic reagents, show how you would convert acetylene and isobutyl bromide to(b) (±)-2,7-dimethyloctane-4,5-diol.