Question

How would you carry out the following conversions? More than one

step is needed in each case.

Short answer

Alkynes are converted into alkenes by reaction with bromine, CH₂Cl₂ and KOH to yield alkynes. These further undergo hydroboration-oxidation reaction to form an aldehyde.

Step-by-step solution

Conversion of alkenes to other compounds

Alkynes are converted into alkenes by reaction with bromine, CH₂Cl₂ and KOH to yield alkynes. These further undergo hydroboration-oxidation reaction to form an aldehyde.

Steps required for carrying out the following conversions

In the first step, styrene reacts with bromine and CH₂Cl₂ to form (1,2-dibromoethyl)benzene. This further reacts with two moles of KOH to form ethynylbenzene. This compound further reacts with BH₃, THF, H₂O₂and ^-OH to form the given compound, 2-phenylacetaldehyde. The reaction can be given as:

Synthesis of first reaction

In the second reaction, styrene reacts with bromine and CH₂Cl₂ to form (1,2-dibromoethyl)benzene. This further reacts with two moles of KOH to form ethynylbenzene. This further reacts with NaNH₂, ammonia and CHBr₃to form prop-1-yn-1-ylbenzene. This compound further reacts with Li in NH₃ to form prop-1-en-1-ylbenzene. The reaction can be given as:

Synthesis of second reaction