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GATE 2021 CY – Question 40

Organic Chemistry · Types of Reactions: Nucleophilic and electrophilic substitution reactions (both aromatic and aliphatic). Addition reactions to carbon-carbon and carbon-heteroatom (N and O) multiple bonds. Elimination reactions. Reactive intermediates – carbocation, carbanion, carbenes, nitrenes, arynes and free radicals. Molecular rearrangements. Barton decarboxylation and Barton-McCombie reaction, Hunsdiecker reaction. · 2 marks · Multiple choice

The major product formed in the following reaction is:

Diagram for GATE 2021 CY question 40
  1. non-6-yn-2-one
  2. non-3-yn-8-one
  3. non-2-yn-6-one
  4. non-3-en-8-one

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Correct answer: (A) non-6-yn-2-one

Explanation

Base initiates the Eschenmoser–Tanabe fragmentation of the α,β-epoxy ketone tosylhydrazone. Loss of the tosylhydrazone-derived nitrogen and cleavage of the adjacent ring bond form an alkyne at one end and a carbonyl at the epoxide-derived end. Tracing the opened carbon chain gives a nine-carbon ketone with the carbonyl numbered 2 and the triple bond at 6: **non-6-yn-2-one, A**.