Question

Identify the lettered compound in the following reaction schemes as per image

Answer 1

(a) In presence of phosphorus tribromide, intramolecular esterification results in cyclization to give lactone A.
The lactone A reacts with alkyne lithium (compound B) to form compound C in which the alkoxide group of lactone A is replaced with alkyne. Thus lactone ring opens and alpha beta unsaturated ketone is obtained.