Visible-Light Photocatalysis of Eosin Y: HAT and Complementing MS-CPET Strategy to Trifluoromethylation of β‑Ketodithioesters with Langlois’ Reagent

A metal-
and oxidant-free photoinduced strategy for thioxo sulfur-selective
trifluoromethylation of β-ketodithioesters at room temperature
is reported. Excellent Z/E-stereoselectivity
has been achieved with cheap and viable Langlois’ reagent (CF3SO2Na, sodium triflinate) in the presence of eosin
Y, which acts as a hydrogen atom transfer (HAT) catalyst. The reaction
proceeds via disulfide intermediate disulfanediylbis­(3-(alkylthio)-1-phenylprop-2-en-1-one)
(a dimer of β-ketodithioester) followed by complementing proton-coupled
electron transfer-mediated reverse HAT cycle of eosin Y. This operationally
simple and efficient protocol allows direct access to triflinated
α-oxoketene dithioacetals in good to excellent yields bearing
diverse synthetically useful functional groups of different electronic
and steric nature.