1. You have been provided with a scheme of R.B. Woodward's 1952 synthesis of the important biomolecule cholesterol. Answer the following questions (attach extra sheets)based upon that synthesis.(41 marks) a. Draw a mechanism for the reaction that occurs from 2 to 3. What is the name of this reaction? There are two alkenes in compound 2 which could act as dienophiles, but only one reacts - give one reason for this observation. (3 marks) b. Write a mechanism for the reaction that occurs from 3 to 4. What is the name of this process? This reaction is an equilibrium process. Explain, using cyclohexane chair conformation, why the product is more stable than the starting material (i.e. the product side of the equilibrium is favoured). (8 marks) c. The reaction of 5 to 6 converts an enol ether to an enone (a,ß-unsaturated carbonyl)by hydrolysis and dehydration. Write a mechanism for this process. (8 marks) d. Write a mechanism for the reaction of 7 to 8. (For clarification, EtO₂CH is called ethylformate, the structure of which you can look up). Comment on why 8 exists in the enol tautomer. (5 marks) e. What is the name of the reaction from 8 to 9? Write a mechanism for this reaction.[EVK is ethyl vinyl ketone, a common abbreviation for pent-4-en-3-one.] (3 marks) f. Show a mechanism for the conversion of 9 to 10. Be sure to account for the elimination of the formyl group (HINT: a by-product of this reaction is formate). (7marks) g. What is the name of the reaction from 10 to 11? What functional group is formed in the reaction going from 11 to 12? (2 marks)

i. What reaction occurs from 24 to 25? Why does a mixture of configurations result at j. Is this an efficient way to make cholesterol? (1 mark)