Synthesis of Angular Pyrrolocoumarins

Abstract

The new pyrrolocoumarin 3 was synthesized in two steps from 7-amino-4-methylcoumarin by selective o-chloroacetylation at position 8 and subsequent cyclization (the Sugasawa route to indoles). Regioselective inverse electron demand Diels-Alder reaction of 3 with dimethyl 1,2,4,5-tetrazine-3,6-dicarboxylate or 3,6-bis(trifluoromethyl)-1,2,4,5-tetrazine then gave the angular pyridazinepyrrolocoumarins 4 and 5, respectively, in good yield.

Key words

antitumour agents - Diels-Alder reaction - electrophilic aromatic substitution - indoles - polycycles

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24

Atomic positions, a full list of bond lengths and angles and other crystallographic data have been deposited as Supplementary Publication No. CCDC 175053. Copies can be obtained from the Cambridge Crystallographic Data Centre, 12 Union Road, Cambridge CB2 1EZ, UK (fax: [phone]; e-mail: [e-mail]).