Microwave‐assisted Rhodium(I)‐Catalyzed C8‐Regioselective C−H Alkenylation and Arylation of 1,2,3,4‐Tetrahydroquinolines with Alkenyl and Aryl Carboxylic Acids

Abstract

Rh(I)‐catalyzed C8‐selective C–H alkenylation and arylation of 1,2,3,4‐tetrahydroquinolines with readily available and inexpensive alkenyl and aryl carboxylic acids under microwave assistance have been realized. Using [Rh(CO)2(acac)] as the catalyst and Piv2O as the acid activator, various 1,2,3,4‐tetrahydroquinolines undergo smooth C8‐selective decarbonylative C–H alkenylation with a wide range of alkenyl carboxylic acids, affording the C8‐alkenylated 1,2,3,4‐tetrahydroquinolines with high efficiency and wide tolerance of functional groups. This method enables the synthesis of C8‐alkenylated 1,2,3,4‐tetrahydroquinolines that would otherwise be difficult to access by means of conventional C–H alkenylation protocols. Moreover, this catalytic system also works well in C8‐selective decarbonylative C–H arylation of 1,2,3,4‐tetrahydroquinolines with aryl carboxylic acids. The catalytic activity strongly depends on the choice of the N‐directing group, with the readily installable and removable N‐(2‐pyrimidyl) group being optimal. The catalytic pathway is elucidated by mechanistic experiments.