= Solution
\b[Warm C with dilute aqueous <acid (chemistry)> to hydrolyse the <iminium ion> to the second <ketone>.] <water> attacks the <iminium> <carbon>, <proton transfers> give a <carbinolamine>, and C–N cleavage releases <pyrrolidine>, present predominantly as its <ammonium> salt in the acidic medium. The two <carbon>–<carbon> bonds constructed in the preceding Michael additions remain intact. This replaces the <iminium> <nitrogen> <substituent> by <oxygen> and gives the diketone D; neither <oxidation> of the skeleton nor <reduction (chemistry)> of the original <ketone> is required.
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