Starting with ethyne, describe how the following compounds can be synthesized:


a. (3S,4R)- 4-bromo-3-hexanol and (3R,4S)- 4-bromo-3-hexanol

Verified step by step guidance

1. <insert step 1> Start with ethyne (acetylene) as your base compound. Ethyne is a simple alkyne with the formula C_2H_2. The goal is to extend the carbon chain to form a six-carbon backbone, which is necessary for synthesizing 4-bromo-3-hexanol.
2. <insert step 2> Perform a series of alkylation reactions to extend the carbon chain. First, convert ethyne into a terminal alkyne by reacting it with sodium amide (NaNH_2) to form the acetylide ion, then react with an appropriate alkyl halide, such as 1-bromopropane, to add three carbon atoms, forming 1-butyne.
3. <insert step 3> Further extend the carbon chain by repeating the alkylation process. Deprotonate the terminal alkyne again using NaNH_2, and react with another alkyl halide, such as 1-bromoethane, to form 1-heptyne, a seven-carbon alkyne.
4. <insert step 4> Hydrogenate the alkyne to form an alkene. Use a Lindlar catalyst to selectively hydrogenate 1-heptyne to (Z)-3-heptene, ensuring the formation of a cis-alkene, which is crucial for the subsequent stereochemistry.
5. <insert step 5> Perform a halohydrin formation reaction. React (Z)-3-heptene with bromine (Br_2) in the presence of water to form the halohydrin. This reaction will yield a mixture of diastereomers, (3S,4R)-4-bromo-3-hexanol and (3R,4S)-4-bromo-3-hexanol, due to the anti-addition of bromine and hydroxyl groups across the double bond.>

Key Concepts

Alkyne Reactivity

Ethyne, or acetylene, is a simple alkyne that can undergo various reactions due to its triple bond. Understanding the reactivity of alkynes is crucial, as they can participate in addition reactions, forming alkenes or alcohols. This knowledge is essential for synthesizing more complex molecules from ethyne.

Stereochemistry

Stereochemistry involves the study of the spatial arrangement of atoms in molecules and how this affects their chemical behavior. The question specifies the stereochemistry of the products, indicating the importance of understanding chiral centers and how to control stereochemical outcomes during synthesis, particularly in the formation of (3S,4R) and (3R,4S) configurations.

Nucleophilic Substitution Reactions

Nucleophilic substitution reactions are fundamental in organic chemistry for introducing new functional groups into a molecule. In the synthesis of the specified bromo-hexanols, understanding how to perform these reactions, particularly with alcohols and alkyl halides, is key to achieving the desired products from the starting material, ethyne.