Eingegangen am 31. Oktober 1986 Pyrano[ 3,4-blindolones 3a-d are available from a-ethoxyalyllactones la, c and disubstituted hydrazines 2a, b without isolation of intermediates. In a two-phase system, however, the intermediate hydrazones 4a, c can be isolated. Conversion of 3a-d into P-carbolines was not possible by lactamisation but via the amides 8 and 9. Indole, 4. Mitt.: 9-Substituierte 4,9-Dihydropyrano[3,4-bKndol-l(3H)-one -Synthese und Urnwandlung in 2,3,4,9-Tetrahydro-lH-pyrido[3,4-b$ndole Die Pyrano[3,4-blindolone 3a-d erhalt man ohne Isolierung von Zwischenprodukten aus den a-Ethoxalyllactonen la, c und den disubstituierten Hydrazinen 2a, b. Setzt man in einem Zweiphasensystem um, so konnen die intermediaren Hydrazone 4a, c aus der organischen Phase isoliert werden. Die fjberfiihrung von 3a-d in p-Carboline gelingt nicht durch direkte Lactamisierung, wohl aber iiber die Amide 8 und 9.
Cleavage and decarboxylation of a-ethoxalyllactones in mineral acid, followed by treatment with arylhydrazines yields a-hydrazonolactones, which produce pyrano [3,4-blindoles under acidic conditions2* 3). These pyranoindoles show interesting pharmacological properties and are valuable starting materials for the synthesis of P-carbolines', 2).
Trying to extend this reaction sequence, we found, that the method described above'), was not suitable for 1,l-disubstituted hydrazines, since the solubility of 2a, b in hot mineral acid was not suficient.
We therefore decomposed la, c in hot mineral acid, extracted the resulting &hydroxy-a-ketoa~id~?~) together with its ester, lactone and other unidentified by-products and treated the residue of the organic layer with the hydrazine hydrochlorides 2a, b in boiling EtOH. Surprisingly this procedure did not lead to the expected hydrazonolactones 4a-c, but furthermore to the corresponding pyranoindolones 3a-d. When, however, 2a reacted, with decomposed la, c in the two-phase system mineral acid/chloroform, the intermediate hydrazonolactones 4a, c migrate into the organic layer, which obviously interrupts the reaction and enables their isolation.