Question

With organolithium and organomagnesium compounds, approach to the carbonyl carbon from the less hindered direction is generally preferred. Assuming this is the case, predict the structure of the major product formed by reaction of methylmagnesium bromide with 4-tert-butylcyclohexanone.

Short answer

Answer: The major product is a tertiary alcohol, where the CH3 group is attached to the carbonyl carbon (now an alcohol carbon) at the 4th position (opposite the tert-butyl group) of the cyclohexane ring.

Step-by-step solution

Draw the structures of the reactants

Firstly, draw the structures of methylmagnesium bromide (CH3MgBr) and 4-tert-butylcyclohexanone.

Identify the carbonyl carbon

In the structure of 4-tert-butylcyclohexanone, find the carbonyl carbon (C=O).

Find the less hindered side of the carbonyl carbon

Determine the less hindered side of the carbonyl carbon. Since the bulky tert-butyl group is attached to the cyclohexanone ring at the 4th position, the less hindered side of the carbonyl carbon will be on the opposite side of the tert-butyl group.

Reaction of methylmagnesium bromide with 4-tert-butylcyclohexanone

Methylmagnesium bromide reacts with 4-tert-butylcyclohexanone by attacking the carbonyl carbon from the less hindered direction. The CH3 group of methylmagnesium bromide adds to the carbonyl carbon, the carbonyl oxygen gets a negative charge, which further reacts with the MgBr, resulting in an alkoxide intermediate.

Predict the major product

The major product will be formed after the alkoxide intermediate reacts with a proton source (often water is used), leading to the protonation of the negatively charged oxygen atom. This results in the formation of a tertiary alcohol with the CH3 group attached to the carbonyl carbon (now an alcohol carbon) at the 4th position (opposite the tert-butyl group) of the cyclohexane ring.