Simple and Efficient Preparation of Reagents for Thiopyran Introduction: Methyl Tetrahydro-4-oxo-2H-thiopyran-3-carboxylate, Tetrahydro-4H-thiopyran-4-one, and 3,6-Dihydro-4-trimethylsilyloxy-2H-thiopyran - Ward, Dale E; Rasheed, M Abdul; Gillis, H Martin; Beye, Garrison E; Jheengut, Vishal; Achonduh, George T (Synthesis, 2007)