Novas alternativas para a síntese de calcogenoindolizinas

Abstract

n the present work it was developed three general methods to prepare different chalcogenindolizines derivatives. The methods basically combine important features of Green Chemistry, which involve the use of alternative energy sources and catalysis, with the aim to provide efficient processes, with low energy demand. Initially, it was prepared the 1-chalcogenindolizines, through a base-promoted intramolecular cyclization of chalcogen-containing pyridinium salts. It is worth to mention that, until the moment, these structures are unprecedented. Thus, through a comparative study between different energy sources; conventional heating (1 h, 70 ºC) and ultrasound irradiation (5 min, 20 kHz), 12 derivatives of the 1-sulfenilindolizines and 2 derivatives of 1-selanilindolizines were prepared in excellent yields. Besides, glycerol, a cheap and biodegradable solvent, was used as a green solvent. In addition, an efficient method for the chalcogenation of indolizines was developed, by using Cu(I) as catalyst and DMSO as solvent. Under ultrasonic irradiation (US, 20 kHz), as an alternative energy source, 16 derivatives of the 3-sulfenilindolizines were synthesized selectively, in moderated to good yields, through a reaction between diorganyl disulfides and 2-arylindolizines. Additionally, diorganyl diselenides were used as substrate, affording 4-derivatives of 1,3-bis-selanilindolizines in very good yields. It is worth to mention that the use of ultrasonic irradiation made the reaction faster and selective, in comparison to conventional heating. Finally, a transition metal-free method was developed for the synthesis of 3 sulfenilindolizine, through the reaction between thiols and 2-arylindolizines. In presence of eosin Y and atmospheric oxygen, 16 derivatives of 3-sulfenilindolizines were satisfactorily prepared, under blue light irradiation (LED, 50W), as an alternative energy source. Additionally, by employing catalytic amounts of I2, the methodology was expanded, affording 6 derivatives of the 1,3-bis-sulfenylindolizines in good yields.