Q.Identify X and Y: CH3-CO-CH2-CH2-COOC2H5, treated with

Step 1. The substrate, CH3-CO-CH2-CH2-COOC2H5 (ethyl 4-oxopentanoate, or 'ethyl levulinate'), carries TWO electrophilic carbonyls: a ketone (C4) and an ester (C1).

Step 2. A ketone carbonyl is significantly more electrophilic, and less sterically/electronically deactivated, than an ester carbonyl (whose carbon is stabilised by resonance donation from the ester oxygen) -- so a single equivalent of CH3MgBr adds SELECTIVELY to the ketone carbon, leaving the ester group untouched at this stage.

Step 3. This addition gives X, the magnesium bromide alkoxide salt at C4: CH3-C(OMgBr)(CH3)-CH2-CH2-COOC2H5 -- a gem-dimethyl tertiary alkoxide, since the incoming Grignard methyl joins the ketone's own methyl on the same carbon.

Step 4. H3O+ work-up (ii) first protonates this alkoxide to the free tertiary alcohol, ethyl 4-hydroxy-4-methylpentanoate, (CH3)2C(OH)-CH2-CH2-COOC2H5.

Step 5. That newly-freed -OH sits exactly four atoms from the ester carbonyl carbon (O-C4-C3-C2-C1), the classic geometry for a favourable 5-membered-ring intramolecular transesterification -- so under the acidic aqueous work-up conditions, the tertiary alcohol cyclises onto the ester, displacing ethanol and closing to the gamma-lactone, Y = 4,4-dimethyldihydrofuran-2(3H)-one (a 5-membered cyclic ester, gem-dimethyl at the carbon farthest from the ring oxygen).

Recognise that a Grignard reagent attacks the MORE electrophilic of two carbonyls first (ketone over ester), then check the resulting hydroxy-ester's geometry for a favourable ring size (5- or 6-membered) that would let it lactonise spontaneously during acidic work-up.

• Assuming the Grignard reagent reacts with the ester group instead (which, with excess RMgX, WOULD eventually give a tertiary alcohol too, but only after first passing through and consuming the ketone) -- with a single equivalent, the more reactive ketone carbonyl is attacked first and essentially exclusively.