The present disclosure generally relates to a process for converting a fused, tricyclic compound to a fused, tetracyclic compound that includes a furan ring therein. More particularly, the present disclosure related to a process for preparing a hydrocodone compound, or a compound structurally related thereto, and in particular (+)-hydrocodone, by subjecting a structurally corresponding sinomenine starting compound to a super acid-assisted furan ring closure reaction.