Q40E - Organic Chemistry (Mcmurry)

Question

How would you carry out the following syntheses?

Step-by-Step Solution

Answer

For conversion of cyclohexene to cyclobutane HBr and lithium dibutyl copper is needed.

For conversion of cyclohexanol to cyclobutane  ${\mathrm{PBr}}_3$and lithium dibutyl copper is needed.

For conversion of cyclohexane to cyclobutane bromine and UV light with lithium dibutyl copper is needed.

Step 1: Alkene reaction with HBr

When HBr is added to an alkene it forms alkyl halides or it can be said as alkyl bromide.

Step 2: Alcohol reaction with PBr 3

When PBr₃ reacts with alcohol, it replaces OH group of alcohol with Br to give an alkyl bromide.

Step 3: Alkane reaction with Br 2 in presence of light

Alkanes react with bromine only in presence of UV light. UV light creates bromine radical which react with alkane to give alkyl bromide.

Step 4: Alkyl halide reaction with lithium dialkyl copper

Alkyl halide and lithium dialkyl copper react with each other to give a higher hydrocarbon chain.

Here in question butyl group has to be added to given hydrocarbon so lithium dibutyl copper will be used as reagent for conversion.

Step 5: Reactions needed for conversion

Reactions needed for conversion to cyclobutane

Here, in reaction of cyclohexene HBr is used for bromination, in cyclohexanol phosphorus tribromide is used and cyclohexane dibromide with UV light is used for bromination. After alkyl bromide formation alkylation is performed using lithium dibutyl copper