A Simple and Efficient Synthesis of Heterocycle-Fused 2H-Thiopyrans, Furo-, Benzofuro-, Thieno-, Benzothieno-, Pyrrolo- and Indolo-2H- thiopyrans, from Heteroaromatic Thioketones and α-Chloroacrylonitrile or α-Bromoacrylic Esters via a Hetero Diels-Alder Reaction-Dehydrohalogenation Process - Saito, Takao; Shizuta, Takuya; Kikuchi, Hideki; Nakagawa, Junko; Hirotsu, Kenji; Ohmura, Haruo; Motoki, Shinichi (Synthesis, 1994)