Synthesis of Trifluoromethylated 4-Pyran and 4-Thiopyran via Divergent Reaction of β-CF-1,3-Enynes with β-Ketothioamides.

A chemodivergent tandem intermolecular hydrocarbonation and intramolecular oxy- or thioheterocyclization sequence of β-CF-1,3-enyne with β-ketothioamides (KTAs) leading to ring-trifluoromethylated 4-pyran or 4-thiopyran, respectively, by the combined use of AgNO as a catalyst and EtN as a base was developed. A remarkable substituent effect was observed. The substituent on either the keto moiety or the nitrogen atom of β-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.