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Question

Identify (X) and (Y) in the following transformation :

The correct answer is

This question is built on drawn structures, so the options cannot be reproduced as text. The chemistry behind the official answer is outlined below.

The sequence is organotin chemistry on a dibutylstannylene fragment. LDA is a strong, bulky, non-nucleophilic amide base: its role is to deprotonate rather than to add, generating a carbanionic centre alpha to tin in intermediate (X).

The second step uses CH2Cl2 with MeLi. MeLi deprotonates dichloromethane to give the chloromethyllithium carbenoid LiCHCl2/ClCH2Li, a classic one-carbon homologating reagent. Reaction of a carbenoid with the organotin intermediate inserts a CH2 unit, so (Y) is the ring-expanded or homologated stannacycle rather than a free stannylene.

The key discrimination among the options is that a genuine tin-carbon double bond, written Sn=CH2, is not the product here: stannenes of that type are extremely reactive and are not isolated under these simple conditions, so options depicting Sn=CH2 for both X and Y do not describe the real transformation.

Per the official final answer key the answer is option (A).

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