IN-SITU VINYLINDOLE SYNTHESIS - DIELS-ALDER REACTIONS WITH MALEIC-ANHYDRIDE AND MALEIC-ACID TO GIVE TETRAHYDROCARBAZOLES AND CARBAZOLES

Tetrahydrocarbazoles have been prepared in one-flask syntheses from in doles, ketones, and maleic anhydride, with acid catalysis. The reactio ns involve a condensation of the indole with the ketone or aldehyde, f ollowed by an in situ trapping of the vinylindole in a Diels-Alder rea ction with maleic anhydride. Depending on which indole is used, this m ay or may not be followed by a double bond isomerization. If the doubl e bond isomerization doesn't occur, the adduct may or may not be acyla ted at the nitrogen by maleic anhydride. 1,2,3,4-tetrahydrocarbazole-1 ,2-dicarboxylic anhydrides have been hydrolyzed to the 1,2-dicarboxyli c acids in good yields. The corresponding 1,2-dicarboxylic acids have been regioselectively decarboxylated at the I-position in excellent yi elds. New results with the use of maleic acid as the dienophile in thi s reaction are also discussed.