LEWIS ACID-CATALYZED REACTIONS OF ALPHA,BETA-UNSATURATED N,N-DIMETHYLHYDRAZONES WITH 1,4-BENZOQUINONE - FORMATION OF INDOLES BY A NOVEL OXIDATIVE REARRANGEMENT

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 £rans-2,3-di-hydrobenzofurans in a highly regioselective [3 + 2] process. When [o-(acylamino)phenyl]propenal N,N-di-methylhydrazones 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. © 1990, American Chemical Society. All rights reserved.