Question

Reaction of 5,5-dimethoxypentan-2-one with methylmagnesium iodide followed by treatment with aqueous acid forms cyclic hemiacetal Y. Draw a stepwise mechanism that illustrates how Y is formed

Short answer

Mechanism

Step-by-step solution

Grignard reagents reaction

The Grignard reagent acts as a nucleophile and attacks the carbonyl carbon to produce the corresponding alcoholic product.

Acetals undergo hydrolysis in presence of an acidic medium and undergo deprotection.

Stepwise mechanism

The Grignard reagent CH₃Mgl adds to the carbonyl yielding the corresponding tertiary alcohol after protonation Deprotection of acetals occur in the presence of acid to yield the corresponding aldehyde Intramolecular cyclization occurs which produces the required product.

Mechanism