Improve Method for Synthesis of 4-Thioaryl-2,3,4-trihydro-1-benzothiopyrans: Acid-induced Stereoselective Intermolecular Cycloaddition of α,β-Unsaturated Aldehydes with Arenethiols - Ishino, Yoshio; Mihara, Masatoshi; Kawai, Hidehito (Synlett, 2001)