Generation of N-(tert-Butoxycarbonyl)indole-2,3-quinodimethane and Its [4+2]-Type Cycloaddition

The two conditions for the preparation of the reactive N-(tert-butoxycarbonyl)indolo-2,3-quinodimethane intermediate were developed by the reaction of the N-(tert-butoxycarbonyl)-2-(1-ethoxycarbonyloxymethylallenyl)aniline with K2CO3 Or Pd-2(dba)(3) in refluxing toluene. The resulting N-(tert-butoxycarbonyl)indolo-2,3-quinodimethane was captured by several alkenyl and alkynyl dienophiles to provide the corresponding tetrahydro- and dihydrocarbazole derivatives.