The haloconduritols are members of a class of compounds called glycosidase inhibitors. These substances possess an array of intriguing biological activity, from antidiabetic and antifungal to activity against HIV virus and cancer metastasis. Stereoisomeric mixtures of bromoconduritol (margin) are commonly used in studies of these properties. One recent synthesis of these compounds proceeds via the bicyclic ethers A and B. (a) Identify the starting materials for a one-step preparation of both of these ethers via a Diels-Alder reaction. (b) Which of the starting molecules in your answer is the diene, and which is the dienophile? (c) This Diels-Alder reaction gives an 80 : 20 mixture of B and A. Explain.