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Thebaine 3 is an opioid structure present in opium alongside morphine. It has no sedative properties, but can react in a Diels-Alder reaction with methyl vinyl ketone to give product 4 . Compound 4 reacts with propylmagnesium bromide to yield compound 5. This compound 5 is then treated with KOH in ethylene glycol to produce etorphine 6, a compound 10000 times more potent than morphine and used to immobilise large animals. methyl vinyl ketone 4n+P 3 (thebaine) i) Draw the structure of compound 4. ii) Draw the structure of compound 5. iii) Suggest a mechanism for the synthetic step from compound 5 to etorphine 6. iv) Give a possible reason why compound 6 is so much more biologically active than 3