Water-DMSO-promoted one-pot synthesis of two new series of dihydropyrrolo[2,3-h]quinolines

Pyrrolo[2,3-h]quinolines are important heterocycles with various biological activities. Here, two new series of dihydropyrrolo[2,3-h]quinolines with more substituents on quinoline ring (4 and 6) were efficiently synthesized via the catalyst-free three-component reaction (3CR) of but-2-ynedioates, 4-aminoindoles and aldehydes or isatins in DMSO-water (volume ratio: 2.5:1) mixture in mild to good yields. A possible mechanism was proposed based on the crucial and promoted effects of water and DMSO in the 3CR, respectively. In addition, it was found that the dihydropyrrolo[2,3-h]quinolines 4 could be quantitatively oxidized into new pyrrolo[2,3-h]quinolines 10 at room temperature using Cu(NO3)2 as oxidant. This work affords efficient synthesis methods for constructing a library of new pyrrolo[2,3-h]quinolines (4, 6 and 10) and is expected to promote the research on the bioactivities of pyrrolo[2,3-h]quinolines.