Question

The major product formed in the following reaction sequence is 

 

• A. (A)
• B. (B)
• C. (C)
• D. (D)

Hint:

Always consider the major transformations in each step of the reaction sequence, including oxidation, nucleophilic attack, and elimination reactions.

Answer 1

The Correct Option is B

The given reaction sequence involves the following steps:

1. Grignard Reaction: The starting compound is cyclohexanone, and it is treated with ethylmagnesium bromide (EtMgBr) in diethyl ether (Et₂O). This Grignard reaction results in the formation of a tertiary alcohol by the nucleophilic addition of the ethyl group to the carbonyl carbon of cyclohexanone.
2. Oxidation with CrO₃: The tertiary alcohol is then oxidized using chromium trioxide (CrO₃) in dichloromethane (CH₂Cl₂). However, tertiary alcohols are generally resistant to oxidation under these conditions, suggesting possible rearrangement or side reactions.
3. Wittig Reaction: The resulting compound undergoes a Wittig reaction with triphenylphosphonium ylide (Ph₃P=CH₂) in tetrahydrofuran (THF). This step results in the formation of an alkene by replacing the carbonyl group with a methylene group (=CH₂).

Based on the above steps, the major product formed will have an alkyl group adjacent to the newly formed double bond.

The major product of the reaction sequence is option (B), as it shows the correct structure in which the ethyl group from the Grignard reagent is attached, and the alkene is formed in the position that best accommodates the stereochemistry and the rearrangements involved in the reaction mechanism.

Thus, the major product is (B).