Synthesis of Trifluoromethylated 4H-Pyran and 4H-Thiopyran via Divergent Reaction of /3-CF3-1,3-Enynes with /3-Ketothioamides

A chemodivergent tandem intermolecular hydrocarbonation and intramolecular oxy-or thioheterocyclization sequence of S-CF3-1,3-enyne with S-ketothioamides (KTAs) leading to ring-trifluoromethylated 4H-pyran or 4H-thiopyran, respectively, by the combined use of AgNO3 as a catalyst and Et3N as a base was developed. A remarkable substituent effect was observed. The substituent on either the keto moiety or the nitrogen atom of S-ketothioamides has a great impact on the chemoselectivity. Enynes possessing electron-withdrawing aryl groups on the alkyne moiety are generally good candidates for the present transformation.