Visible-light-induced metal-free cascade cyclization of N-arylpropiolamides to 3-phosphorylated, trifluoromethylated and thiocyanated azaspiro[4.5]trienones

Abstract

Photocatalytic strategies for the preparation of 3-phosphoryl/trifluoromethyl/thiocyanato azaspiro[4.5]trienones via a radical-initiated cascade annulation reaction of N-arylpropiolamides with phosphorus reagents, 1-trifluoromethyl-1,2-benziodoxol-3(1H)-one (Togni's reagent II) or NH₄SCN have been developed under blue LED irradiation at room temperature. The novel synthetic methodologies constitute the first application of 2,4,5,6-tetra(9H-carbazol-9-yl)isophthalonitrile (4CzIPN) as a photocatalyst for the synthesis of spiro-γ-lactam derivatives, in which the use of transition metals and a high reaction temperature could be avoided. The reactions are operationally simple, easy to scale up, and metal-free with wide reaction scope and good functional group tolerance.