Tri- and tetracyclic heteroaromatic systems: Synthesis of novel benzo-, benzothieno- and thieno-fused pyrano[2,3-c]pyrazol-4(1H)-ones
Eller, GA; Eller, GA; Haring, AW; Haring, AW; Datterl, B; Datterl, B; Zwettler, M; Zwettler, M; Holzer, W; Holzer, W
A straightforward, two-step synthesis of chromeno[2,3-c]pyrazol-4(1H)-ones, thieno[2',3':5,6]pyrano[2,3-c]pyrazol-4(H-1)-ones, and [I]benzothieno[2',3':5,6]pyrano[2,3-c]pyrazol-4(H-1)-ones, respectively, is presented. Hence, treatment of I-substituted or 1,3-disubstituted 2-pyrazolin-5-ones with 2-fluorobenzoyl chloride, 2-chlorobenzoyl chloride, 3-chlorothiophene-2-carbonyl chloride, or 3-chloro-1-benzothiophene-2-carbonyl chloride using calcium hydroxide in refluxing 1,4-dioxane gave the corresponding 4-aroylpyrazol-5-ols, which were successfully cyclized into the fused ring systems (NaH/DMF). The N-unsubstituted title compounds were obtained upon treatment of 1-(4-methoxybenzyl) protected congeners with trifluoroacetic acid. Detailed NMR spectroscopic investigations (H-1, C-13, N-15) with the obtained compounds were undertaken.<
