The first total syntheses of (±)-montanin A and (±)-teuscorolide have been achieved from an advanced precursor previously developed via a Diels–Alder strategy; in the synthetic sequence, the synthesis of montanin A was first accomplished in 8 steps, from which teuscorolide was readily achieved in 2 steps by using a novel furan oxidative cyclization–retro-cyclization process as a key operation.