Efficient Synthesis of 3,6‐Dihydro‐2H‐pyrans via [3+2+1] Annulation Based on the Heteroatom‐free Tri‐atom Donor

A new [3+2+1] annulation strategy based on the heteroatom‐free tri‐atom donor to synthesize 3,6‐dihydro‐2H‐pyrans has been developed. In this method, 2‐arylpropylene served as tri‐atom donor to contribute three carbon atoms, the heteroatom was provided by aldehyde, and DMSO served as one carbon donor and solvent. This annulation reaction gave 3,6‐dihydro‐2H‐pyrans in moderate to good yields. Based on the control experiments, a possible mechanism was proposed.