Functional groups installing adjacent

The answers to these questions dictate what must be done. Specifically, we must install two adjacent functional groups. This suggests that we consider using a ring-opening reaction of an epoxide. Using a retrosynthetic analysis, we draw the epoxide that would be necessary. 

By way of review, the Prins reaction (Scheme 8.20) comprises addition of a carbonyl group to an olefin followed by capture of a nucleophile by the other end of the double bond (20-1). A side reaction consists of addition of carbonyl oxygen (20-2). Yet another photolysis, this one on 19-5, severs the bond between the carbonyl and the adjacent quaternary carbon atom to the unsaturated aldehyde 21-1 (Scheme 8.21) this is admixed with the product of 21-2 from addition via oxygen. Treatment of the mixmre of these products with mild acid leads to intramolecular Prins condensation of the aldehyde in 21-1 with the C13-C14 double bond. Capture of a nucleophile, in this case water, from the less hindered face installs the critical 14a-hydroxyl function. The (9-addition product 21-2 presumably cycles back to 21-1, which the goes on to product. The 12)8-hydroxy product predominates over its 12a-isomer in a 2 1 ratio. 

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