US EPA

6619800 

Journal Article 

SYNTHESIS OF NEW 3-SUBSTITUTED 2H-THIOPYRAN DERIVATIVES VIA [4+2] CYCLOADDITION REACTIONS USING ACCEPTOR SUBSTITUTED ENAMINOTHIONES 

Dietrich, U; Feindt, A; Pulst, M; Weissenfels, M; Greif, D; Cao, W; , 

1994 

Journal für Praktische Chemie. Chemiker-Zeitung
ISSN: 0941-1216 

JOHANN AMBROSIUS BARTH VERLAG 

HEIDELBERG 

434-438 

WOS:A1994NX58700009 

3- and 4-Nitro acetophenones as well as 3- and 4-trifluoromethyl acetophenones react with POCl3/DMF (Vilsmeier reagent) to give dimethyliminium perchlorates 1a-d after addition of perchloric acid to the reaction mixture. Substitution of the chloro atom in 1 by using sodium sulfide nonahydrate occurs under mild conditions (in case of nitro compounds at -5-degrees-C) leading to enaminothiones 2a-d. Reactions with acroleine and methylvinylketone in refluxing benzene give exclusively 2H-thiopyran derivatives 4a-h, which were isolated in good yields after spontaneous fast elimination of dimethylamine. In contrast, the introduction of 1-nitro-2-phenylethene as the dienophile allows stepwise reaction to give stable adducts 3k and 3l, respectively, and also 3m under mild conditions (reaction at room temperature). H-1 n.m.r. spectroscopic data as well as the elimination of dimethylamine to 4k-m permit the elucidation of the structure of adducts 3k-m.