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A series of methyl 9H-pyridazino[3,4-b]indole-3-carboxylates and related compounds were synthesized using a Diels-Alder reaction of methyl 3-(1H-indol-3-yl)-2-propenoates and dibenzyl azodicarboxylate. Several compounds were found to have high affinity for the benzodiazepine receptor. Their structure-activity relationships are discussed.

Oxidation of 3-alkoxycarbonyl-substituted pyrrolic compounds with aqueous potassium ferricyanide in the presence of potassium hydroxide afforded 2,2′- and 5,5′-bispyrrolenine derivatives, which were in equilibrium with each other in solution via radical intermediates. The substituent effects on the dimer formation will also be discussed in connection with the characters of the intermediate pyrryl radicals.

The thermochromic properties of the dimers in solution, obtained by oxidation of 3-carbonyl substituted pyrroles, was determined as being due to the reversible dissociation into pyrryl radicals. The structure and character of the pyrryl radicals are discussed on the basis of substituent effect on thermochromism and ESR studies.