Question

Show two methods to synthesize each alkene: a one-step method using a Wittig reagent, and a two-step method that forms a carbon–carbon bond with an organometallic reagent in one of the steps.

a.

b.

Short answer

a.

b.

Step-by-step solution

Synthesis of alkenes

Wittig reaction would convert an aldehyde or ketone into alkene using a triphenyl phosphonium ylide. Similarly, organometallic compounds, such as Grignard reagent, are good nucleophiles that would attack carbonyl carbon.

The hydrolysis followed by dehydration would yield a mixture of corresponding alkenes.

Synthesis of given compounds

a. 2-methylpent-3-one would give a single alkene with the Wittig reagent while forming a mixture of alkenes using an organometallic reagent.

The mixture of alkenes would include a tri-substituted major product and a di-substituted minor product.

Conversion to alkene

b. Cyclopentanone reacts with triphenyl phosphonium ylide to give an alkene while reacting with ethyl phenyl magnesium bromide. This is followed by a dehydrating agent such as sulfuric acid to form a mixture of alkenes.

Synthesis of alkenes via two methods