Photocatalysis Applied to the Synthesis of N-heterocycles: New Strategies for Intercepting Radical Intermediates Generated in Processes Promoted by Visible-light-Tris (trimethylsilyl)silane Combination.

Abstract

The development of sustainable synthetic strategies that rapidly achieve the synthesis of (new) molecules with pharmacological or technological interest is one of the biggest challenges in the contemporaneous organic synthesis. The use of light to promote chemical transformations consist in great appeal in this regard, since light is the cleanest source of energy, and the sunlight stands out as an endless source. In this context, photocatalysis and photoredox catalysis have been gaining more attention in organic synthesis labs over the years. Our proposal consists in the development of photochemical strategies based on a protocol recently reported by our group. In these strategies, we will apply tris(trimethylsilyl)silane (TTMSS) and visible light irradiation to initiate the radical cascade process for the synthesis of a range of heterocyclic scaffolds. To this goals, two photochemical cyclization strategies promoted by TTMSS/visible light will be developed. In the first one, enamides derived from 2-iodo-aniline are going to be converted to functionalized amino-indolines and amino-oxindols through a radicalar cyclization reaction followed by oxidation of the radical intermediate and finally the attack of a nucleophile. In the second one, enamines generated in-situ from aldehydes also derived from 2-iodo-aniline and a chiral amine organocatalyst will be subject to the same radical cyclization process and oxidation, in order to access chiral 3-carbonyl-indolines and 3-carbonyl-oxindols. Furthermore, the concept will be extended an addition-cyclization strategy with maleimides (process that may be considered as a formal [4+2] cycloaddition). From this cascade reaction, densely functionalized tetrahydroquinolines will be achieved in a one-pot way. Finally, our attention will be turned toward the development of a cascade protocol that involves a photoredox cyclization followed by a cross-coupling protocol catalyzed by Iridium and Nickel respectively. In this strategy, alkenes and alkynes derived from 2-iodo-aniline will be convert to benzylic oxindoles and indoles, correspondingly.All designed N-heterocyclic frameworks are of great interest, once they are in close relation to systems founded in alkaloids and drug structures. It's also worth to emphasizing that, photochemistry, photoredox catalysis, organocatalysis and nickel catalyzed reactions are hot-topics and of great interest of both academia and industries. However, they are still less explored by the Brazilian community.