Efficient Synthesis of Substituted Tetrahydrothiopyrano[2,3-b]thiopyran-4,5-diones by a Double Annulation Strategy from Dialkenoylketene Dithioacetals - Pan, Wei; Dong, Dewen; Ouyang, Yan; Wu, Rigenhada; Yang, Yang; Liu, Qun (Synthesis, 2007)