Cu(II)-Catalyzed [3 + 1 + 1] Cascade Annulation of Sulfoxonium Ylides with 2-Naphthols and N , N -Dimethylaminoethanol as a C1 Synthon: Direct Access to Naphtho[2,1- b ]furans

We report a Cu(II)-catalyzed [3 + 1 + 1] cascade annulation for the synthesis of naphtho[2,1- b ]furan derivatives from readily available β-ketosulfoxonium ylides and 2-naphthols, using N, N -dimethylaminoethanol (DMEA) as both a solvent and a one-carbon synthon. The transformation proceeds under mild, air-tolerant conditions and affords the desired products in good to high yields with broad functional group tolerance. This protocol accommodates a wide range of substrates and is amenable to gram-scale synthesis, highlighting its practicality. Moreover, the resulting naphthofuran derivatives exhibit tunable photophysical properties, indicating their potential applications in materials and medicinal chemistry.