Making use of a Diels–Alder approach based on various α,β-unsaturated 2-carbomethoxy-4,4-dimethyl-1-tetralones as novel dienophiles, the corresponding polycyclic adducts could be efficiently synthesized in good to high yields (74~99%) in the presence of Lewis acid (e.g., SnCl4). Accordingly, a synthetically useful platform is established to provide a focused aromatic polyketide-like library for screening of potential natural and non-natural antimicrobial agents.