Lewis Acid Catalyzed Reactions of α,β-Unsaturated N,N-Dimethylhydrazones with 1,4-Benzoquinone. Formation of Indoles by a Novel Oxidative Rearrangement

Article abstract of DOI:10.1021/jo00301a009

The Diels-Alder reaction of quinones and (E)-3-arylpropenal N,N-dimethylhydrazones only proceeds with 1,4-naphthoquinone as the dienophile.The addition of Lewis acids leads to the formation of trans-2,3-dihydrobenzofurans in a highly regioselective <3+2> process.When propenal N,N-dimethylhydrazones 4 and 5 were allowed to react with 1,4-benzoquinone and boron trifluoride, an unprecedented oxidative rearrangement took place yielding indole-3-carboxaldehyde N,N-dimethylhydrazones 7 and 8, respectively.