A novel method for the synthesis of  5-aryl-2-methylthio-4H-pyran-4-ones 4a-h has been developed from the  corresponding cinnamoylketene dithioacetals 1a-h in three successive steps.  In the first step, 1a-h were oxidized with alkaline hydrogen peroxide to  give the corresponding (β-aryl-,α,β-epoxypropanoyl)ketene dithioacetals  2a-h in 78-89% overall yields. In the second step the epoxyketones  2a-h were subjected to rearrangement in the presence of ether-boron  trifluoride complex to give the corresponding  (α-formyl-α-phenylacetyl)ketene dithioacetals 3a-h, which were then  cyclized in the third step by refluxing in acetic acid/ethanol to afford the  title compounds in good yields.
                                    从相应的
肉桂烯酮二
硫代
乙醛 1a-h 开始,分三个步骤合成了 5-芳基-2-甲
硫基-4H-
吡喃-4-酮 4a-h 的新方法。  第一步,用碱性
过氧化氢氧化 1a-h,得到相应的(δ-芳基-,δ±,δ-环氧丙酰基)烯酮二
硫代
乙醛 2a-h,总产率为 78-89%。在第二步中,环氧酮 2a-h 在醚-
三氟化硼络合物存在下进行重排,得到相应的(δ-甲酰基-δ-
苯乙酰基)烯酮二
硫代
乙醛 3a-h,然后在第三步中通过在
醋酸/
乙醇中回流环化,以良好的收率得到标题化合物。