A divergent synthesis of functionalized unsaturated δ-lactones 2, 3, 4, and 5 has been developed starting from the readily available α-alkenoyl-α-carboxyl ketene dithioacetals 1 in high to excellent yields under mild reaction conditions. Thus, 6-substituted 3-(1, 3- dithiolan/dithian-2-ylidene)-3 H-pyran-2 (6 H)-ones 2, obtained from a consecutive reduction with NaBH4 and acidic workup of 1 via a novel vinylogous Pummerer cyclization, can be ...
