Question

The major product in the following reaction is:

Cl

1. CH$_3$MgBr, dry either, 0°C
2. aq. acid O CH$_3$

• A. H$_3$C O CH$_3$
• B. OH
• C. CH$_3$

Answer 1

Answer: (C)

2,2-dimethyltetrahydrofuran

Answer 2

The reaction proceeds in two main steps. First, the Grignard reagent (CH$_3$MgBr) performs a nucleophilic addition to the ketone carbonyl group, forming an alkoxide intermediate. Second, this alkoxide undergoes an intramolecular SN2 reaction by attacking the primary alkyl chloride, leading to the formation of a stable 5-membered cyclic ether (2,2-dimethyltetrahydrofuran). The final aqueous acid workup protonates any remaining alkoxide or hydrolyzes the Mg-complex but does not alter the cyclic ether.