Síntese regiosseletiva de cromenos e cromenonas derivados de organocalcogênio via reações de ciclização intramolecular

Abstract

In the first part of this work, a series of organochalcogen propargyl aryl ethers (19 examples) was easily prepared by reaction of propargyl aryl ethers and different organochalcogen electrophilic species. In general, the ethers were satisfactorily obtained in 50 to 80% yield. After that, the organochalcogen propargyl aryl ethers were submitted to intramolecular electrophilic cyclization reaction, using iodine and tellurium electrophilic reagents. Through this methodology, we were able to obtain a wide range of 4-organochalcogen-2H-chromenes (26 examples), regioselectively, in 40 to 83% yield. In order to evaluate the versatility of the obtained 2H-chromenes as precursors to the synthesis of different functionalized chromenes, the 3-iodo-4-(n-butylseleno)-2H-chromene was submitted to palladium-catalyzed Negishi coupling reactions with different organozinc reagents and, to CuI-catalyzed coupling reaction with arylthiols. The corresponding 3-aryl-4-(n-butylseleno)-2H-chromenes (3 examples), obtained from Negishi coupling, as well as the 3-arylthio-4-(n-butylseleno)-2H-chromenes (3 examples) were isolated in 65 to 91% yield. In a second stage, we developed an alternative and regioselective method to promote the intramolecular cyclization of alkynyl aryl ketones, by employing FeCl3 and differently substituted diorganyl diselenides as promoter agents of this process. Through this cyclization protocol we could satisfactorily synthesize a series of 3-organochalcogen-4H-chromen-4-ones (26 examples, in 60 to 87%), using relatively mild reaction conditions, since all the experiments were carried out at 25 °C, under ambient atmosphere.