Lewis acid-promoted reactions of styrenyl systems with benzoquinone bisimines: New regioselective syntheses of substituted 2-aryl-2,3-dihydroindoles and 2-arylindoles

BF3-promoted reactions of 2-alkoxy-1-(N-benzoyl)-4-(N-benzenesulfonyl)-1,4-benzoquinone bisimines (2/3) with beta-methylstyrenes yield trans-5-(N-benzoylamino)-6-alkoxy-2-aryl-3-methyl-2,3-dihydroindoles (4/5) or 3-(N-benzoylamino)-6-aryl-7-methyl-4,8-dioxobicyclo[3.2.1]oct-2-enes (6) regio- and stereoselectively. The former are produced in reactions with styrenes bearing alkoxy substituents, whereas with neutral or electron deficient styrenes, the latter are found. As applications of this new methodology to the synthesis of biologically interesting molecules, reactions of 2H-chromenes and 7-methoxy-N-toluenesulfonyl-1,2-dihydroquinoline with the bisimines have been developed as routes to substituted aza- and diazapterocarpans. Syntheses of 2-arylindoles via oxidation of the dihydroindoles 4 are also reported.