As traditional small-molecule drug discovery programs focus on a relatively narrow range of chemical space, most human proteins are viewed as unreachable targets. Consequently, there is a strong interest in expanding the chemical space in drug discovery beyond traditional small molecules. Here, a strategy for the preparation of a broad natural-product-like macrocyclic library by using the tandem allylic oxidation/oxa-conjugate addition and macrocyclization reactions is reported. Cheminformatic analyses demonstrate that this tetrahydropyran-containing macrocyclic library shows a significant overlap with natural products in the chemical space. This approach can be used for designing libraries that may probe more deeply into natural-product-like space.