U. Pindur and M. Rogge, “New [4 + 2] Cycloadditions of in situ Generated Indolyl Enol Ethers and Their Anions with Dimethyl Acetylenedicarboxylate: A One-Pot Access to 4-Alkoxy-Substituted Carbazoles”, Chimia, vol. 46, no. 11, p. 441, Nov. 1992.