Design and Synthesis of Novel Chiral Iodine(III) Reagents and their Enantioselective Applications

Abstract

Chiral iodoarene catalysts have become an environmentally and chemically green alternative to transition metal-based catalysts due to their facile availability, low toxicity, versatile reactivity, high stability towards moisture and oxygen atmosphere, ease of recovery, and ease of handling. Some of the oxidation reactions tend to use chiral iodine catalysts because of their strong electrophilicity, appreciable oxidizing properties and its ability to induce a wide range of stereoselective transformations under mild reaction condition with a high degree of stereocontrol. High reactivities and selectivities for central iodophenol lactate-based catalysts have been reported. Here, novel chiral iodoarene lactate-based catalysts were synthesized where the oxygen atom in the previous versions of these catalysts has been replaced with a protected nitrogen atom. The new family of central chiral iodoarenes catalysts were successfully and easily designed and synthesized over several steps in good yields starting with the protection reaction of iodoaniline derivatives followed by Mitsunobu reaction conditions in the last stage of the synthesis. The reactivities and enantioselectivities of the newly synthesized iodoaniline catalysts have been studied in several stereoselective oxidative transformations such as α-oxysulfonylation of ketones, oxidative rearrangement of alkenes, oxylactonization of carboxylic acid, and dearomatization of phenols. In addition, the structural features of the prepared iodoaniline catalysts were investigated by NMR spectroscopy analysis and X-ray crystallographic studies. Finally, a novel methodology was explored for the oxidative rearrangement of non-terminal alkynes to produce α-arylalkanoic esters. The optimized conditions were very selective to rearranged activated non-terminal alkynes bearing electron donating groups (MeO) at the ortho and para positions of aryl alkynes. Hypervalent iodine reagents were utilized to rearrange the alkynes effectively in high yields in racemic form. Then, chiral α-arylalkanoic ester were synthesized successfully in high yields 60-92% and selectivities 62-99% ee, when C2−hypervalent iodine reagent bearing electron donating lactamides side chain was used in the reaction. The reaction was scaled up successfully for organic synthesis applications. Also, the reduced chiral iodoarene was recycled for sustainable and environmental properties. After that, the efforts were directed to perform the reaction catalytically, but the maximum yield obtained was 20%. A possible mechanism was proposed and described based on the isolated products and control experiments.