Unexpected formation of quinolone derivatives in Reissert indole synthesis

The Reissert indole synthesis was found to unexpectedly give 3-hydroxy-1,2, 3,4-tetrahydro-2-quinolone derivative 4, sometimes in a high ratio with the expected ethyl indole-2-carboxylate derivatives 3 in a low ratio, dependin g on the conditions of the catalytic reduction of the intermediate 2-nitrop henylpyruvate 2. This reactivity is characteristic in the preparation of 7- substituted indoles.