Show how you would convert
d. but-1-yne to cis-hex-3-ene.

Verified step by step guidance

1. Step 1: Begin by identifying the functional group in but-1-yne. It contains a terminal alkyne group (-C≡C-H). The goal is to extend the carbon chain and convert the alkyne into a cis-alkene.
2. Step 2: Perform a hydroboration reaction to add a boron atom to the terminal alkyne. Use a reagent like disiamylborane (R2BH) to selectively add boron to the terminal carbon. This step prepares the molecule for further functionalization.
3. Step 3: Oxidize the boron intermediate using hydrogen peroxide (H2O2) in a basic solution (NaOH). This converts the boron group into an alcohol (-OH) at the terminal carbon, resulting in an aldehyde (butanal).
4. Step 4: Perform a Wittig reaction to extend the carbon chain. React the aldehyde with a phosphonium ylide (Ph3P=CHCH2CH3) to form hex-3-yne. This reaction adds three carbons to the molecule and introduces a triple bond at the desired position.
5. Step 5: Hydrogenate hex-3-yne using a Lindlar catalyst (Pd/CaCO3, poisoned with quinoline) to selectively reduce the triple bond to a cis-double bond, yielding cis-hex-3-ene as the final product.

Key Concepts

Alkyne to Alkene Conversion

The conversion of alkynes to alkenes typically involves a reaction known as hydrogenation, where hydrogen gas is added across the triple bond of the alkyne. This process can be facilitated by catalysts such as palladium or platinum, which help to break the triple bond and form a double bond, resulting in an alkene. In this case, but-1-yne will be transformed into an alkene intermediate before further reactions can yield the desired product.

Stereochemistry and Cis-Trans Isomerism

Cis-trans isomerism is a form of stereoisomerism where the spatial arrangement of groups around a double bond affects the properties of the molecule. In cis isomers, similar groups are on the same side of the double bond, while in trans isomers, they are on opposite sides. Understanding this concept is crucial for converting the alkene intermediate into cis-hex-3-ene, as the reaction conditions must favor the formation of the cis isomer.

Reagents for Stereoselective Reactions

To achieve the specific stereochemistry required for cis-hex-3-ene, certain reagents and conditions must be employed. For example, the use of specific catalysts or reagents that promote syn-addition during the hydrogenation process can lead to the formation of the cis isomer. Familiarity with these reagents and their mechanisms is essential for successfully directing the reaction towards the desired stereochemical outcome.