Problem $3.$ a$)$ Provide a sequence of steps that leads to the product on the right. What stereochemistry should

you start with at the labeled center? $($Bonus: try to explain the stereochemistry$)$

b$)$ One of the free $OH$ groups is more reactive than the other. Which one? Hint: what is the most stable

conformation?

Problem $4.$ Provide the structures of compounds A$,$ B$,$ C and D and draw a mechanism for their formation.