From phenylacetylphenylacetic acids to indoles: a simple new divergent synthesis of 6,11-dihydro-5H-benzo[a]carbazol-5,6- diones and 6,11-dihydro-5H-benzo[b]carbazol-6,11-diones Jacobo Cruces, Elena Martõ Ânez, Mo Ânica Treus, Luis A. Martõ Ânez, Juan C. Este Âvez, Ramo Ân J. Este Âvez p and Luis Castedo Departamento de Quõ Âmica Orga Ânica e Unidade Asociada C.S.I.C.), Universidade de Santiago de Compostela, 15706 Santiago de Compostela, Spain Received 17 May 2001; revised 21 January 2002; accepted 21 February 2002 Abstract ÐThe synthesis 6,11-dihydro-5H-benzo[a]carbazole-5,6-diones and 6,11-dihydro-5H-benzo[b]carbazole-6,11-diones from common starting materials, 1-2 0 -nitrophenylacetyl)phenylacetic acids is described. q 2002 Elsevier Science Ltd. All rights reserved. Numerous methods have been developed for the synthesis of indoles due to the importance of compounds that incor- porate the indole subunit. However, the search for new methods for the simple and ef®cient construction of the indole ring system continues to be an important synthetic goal. 1 Of particular interest are methods for the synthesis of polycyclic indoles, including benzo- or pyrido-fused carbazoles, because of their potential in the development of antitumor agents. 2 Antineoplastic activity in these compounds has been attributed 3 to their ring systems, which contain an embedded 2-phenylnaphthalene-like structure in a planar conformation. Interesting examples are benzo[a]carbazoles which, besides having industrial applications as colorants, 4 are known carcinogens with anti- arrhythmic, antimicrobial and antitumoral activity, 5 and are also related to indolo[2,3-a]quinolizine alkaloids. 6 Benzo[b]carbazoles 7 are closely related to pyrido[b]carba- zoles, 2b which have well documented antitumour properties, and examples include elliptinium, a compound used for treatment of thyroid, breast and kidney cancer. Neverthe- less, oxidized derivatives like benzo[a]carbazolequinones 1 Scheme 1) have received very little attention to date and, in the course of our studies on these compounds, only one recent synthesis has been described. 8 In contrast, benzo[b]- carbazolequinones 2 have been the object of great synthetic interest in the past decade because they were related to the kynamicin family of antibiotics. 9 The antitumour activity of these compounds has also been established. 10 Tetrahedron 58 2002) 3015±3019 Pergamon TETRAHEDRON 0040±4020/02/$ - see front matter q 2002 Elsevier Science Ltd. All rights reserved. PII: S0040-402002)00192-8 Keywords: carbazolequinone; indole; phenylacetylphenylacetic acid. p Corresponding author. Tel.: 134-981-563100x14242; fax: 134-981-591014; e-mail: qorjec@usc.es Scheme 1. Retrosynthetic scheme for the syntheses of benzo[a]carbazolequinones and benzo[b]carbazolequinones.