Alcohols react with dihydropyran in the presence of acid to give products of general struc...

Alcohols react with dihydropyran in the presence of acid to give products of general structure I, rather than II. Note that I is an acetal.

(a)    Explain why I is formed in preference to II. (Hint: Consider the structures of the two carbocations that would form by protonation of dihydropyran at either alkene carbon.)

(b)    From what alcohol and dihydropyran can the compound shown be synthesized?