A general [5+1] annulation reaction, which utilized 4-bromo- or 4-mesyloxy-but-2-enyl peroxides as unique five-atom bielectrophilic synthons to participate in the C–C and the subsequent umpolung C–O bond-forming reactions with C1 nucleophiles, has been developed for the facile synthesis of 2,2-disubstituted dihydropyrans in high yields under mild basic conditions. The dihydropyrans, which are readily prepared on a gram scale by this new method, can be flexibly transformed into the biologically important tetrahydropyrans and pyranones in 1–2 steps.