The products X and Y in the following reaction sequence are
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1. Birch reduction of benzene rings with electron-donating groups (like $-\text{OCH}_3$, $-\text{CH}_3$) gives non-conjugated 1,4-dienes with the substituent on the double bond.
2. Carbenes are highly electrophilic and always show a strong preference for adding to the more substituted or electron-rich double bond in a molecule.
Step 1: Understanding the Concept:
This problem involves two distinct organic reactions:
1. Birch Reduction: The reduction of aromatic rings using alkali metals in liquid ammonia. The regioselectivity depends on whether the substituent is electron-donating or withdrawing.
2. Carbene Addition: The reaction of a carbene (\(:CBr_2\)) with an alkene to form a cyclopropane ring. Step 2: Detailed Explanation: Step 1: Formation of X (Birch Reduction):
Anisole (methoxybenzene) has a methoxy group (\(-OCH_3\)), which is electron-donating via resonance (\(+M\) effect).
In Birch reduction, electron-donating groups direct the reduction to the 2,5-positions. The carbon attached to the methoxy group remains unreduced.
Product X is 1-methoxycyclohexa-1,4-diene. Step 2: Formation of Y (Carbene Addition):
The reagents \(CHBr_3\) and \(EtONa\) generate dibromocarbene (\(:CBr_2\)) via \(\alpha\)-elimination.
Dibromocarbene is an electrophilic carbene. It will selectively add to the more electron-rich double bond of the diene X.
In 1-methoxycyclohexa-1,4-diene, the double bond bearing the methoxy group (\(C_1=C_2\)) is significantly more electron-rich than the isolated double bond due to the \(+M\) effect of the oxygen.
Therefore, the carbene adds exclusively to the substituted double bond to form a fused dibromocyclopropane ring.
Product Y is 1,1-dibromo-2-methoxybicyclo[4.1.0]hept-3-ene.
These structures correspond to Figure A. Step 3: Final Answer:
The major products X and Y are shown in Figure A. The correct option is (A).
