Oxalylacetylenes as Dielectrophiles for Annulation of Quinoline Ring: Synthesis of Highly Functionalized 1,3-Oxazinoquinolines

Oxalylacetylenes act as dielectrophiles in the annulation of quinolines with highly functionalized 1,3-oxazine cycle decorated by the ethynyl, oxalyl, ester and aryl substituents. The annulation proceeds under mild condition (room temperature, without catalysts) in 2:1 mode with respect to acetylene and quinoline to deliver 1,3-oxazinoquinolines in 45-88% yields. A beneficial feature of the reaction is that, in contrast to results on the reaction of quinolines with trifluoroacetylacetylenes in the presence of water, where H2O acted as a third electrophile, this reaction well tolerates the aqueous medium. This reaction tolerates also isoquinoline and phenanthridine.

Construction 7-membered ring via Ni–Al bimetal-enabled C–H cyclization for synthesis of tricyclic imidazoles

The construction of 7-membered ring via direct C7–H cyclization of benzoimidazoles with alkenes would provide a more atom- and step-economical route to tricyclic imidazoles and derivatives that widely exist in a broad range of bioactive molecules. However, transition metal-catalyzed C–H cyclization for medium-ring synthesis has been limited to reactive C–H bonds, instead, the activation of unreactive C–H bonds towards medium synthesis still remains an elusive challenge. Herein, we report a direct construction of 7-membered rings via Ni–Al co-catalyzed unreactive C7–H cyclization of benzoimidazoles with alkenes, providing a series of tricyclic imidazoles in 40–98% yield and with up to 95:5 er.

Construction 7-Membered Ring via Ni-Al Bimetal-Enabled C-H Cyclization for Synthesis of Tricyclic Imidazoles

The construction of 7-membered ring via direct C7−H cyclization of benzoimidazoles with alkenes would provide a more atom- and step economical route to tricyclic imidazoles and derivatives that widely exist in a broad range of bioactive molecules. However, transition metal-catalyzed C−H cyclization for medium-ring synthesis has been limited to reactive C−H bonds, instead, the activation of unreactive C−H bonds towards medium synthesis still remains an elusive challenge. Herein, we report a direct construction of 7-membered rings via Ni−Al co-catalyzed unreactive C7−H cyclization of benzoimidazoles with alkenes, providing a series of tricyclic imidazoles in 40−98% yield and with up to 95:5 er.