Cyclohexane derivative formation of carambolaflavone using a Lewis acid catalyst

The scheme below summarizes the results from a study into the optimum conditions needed for a key step in the synthesis of the proposed structure of carambolaflavone, a natural product that has antidiabetic properties. Note that $$\ce{Sc^3+}$$ acts as a Lewis acid in these reactions.

I'm very confused about how the acid is coordinating to the Benzene derivative here?

• The Sc3+ may bind to the benzene derivative but that is not important. The binding to the oxygen of the tetrahydropyran is what matters. – Waylander May 3 '19 at 8:13
• Hi thanks for your answer, but I'm afraid I'm not quite understanding what you mean? – J. Deans May 3 '19 at 9:26
• The key intermediate in the reaction step is an oxonium species R-O=R+ created by the Scandium ion binding to the acetal oxygens on the tetrahydropyan ring. In the first step it binds to the carbonyl of OAc gruop, in the second step to the oxygen of the THP-OPh – Waylander May 3 '19 at 9:42
• Brill, thanks a mill! – J. Deans May 5 '19 at 22:14