Banca de DEFESA: VIRGINIA CAMILA RUFINO

Uma banca de DEFESA de DOUTORADO foi cadastrada pelo programa.
STUDENT : VIRGINIA CAMILA RUFINO
DATE: 20/10/2023
TIME: 14:00
LOCAL: SALA 3.15 BLOCO C - DCNAT
TITLE:

Computational study of a,b-unsaturated enones conjugated addition asymmetric organocatalysis and organic acid effects in the imines formation

KEY WORDS:

Amino-thioureas; Imines; Iminophosphorane-thioureas; Design; DFT.

PAGES: 174
BIG AREA: Ciências Exatas e da Terra
AREA: Química
SUBÁREA: Físico-Química
SUMMARY:

Theoretical methods are an important tool in elucidating reaction mechanisms and understanding experimental results. We can also use them to exclude mechanisms and infer about experimental observations, such as the presence of traces of a contaminant that, as for some of the reactions investigated here, has a potential catalytic effect. Increasingly, these methods are useful for the rational design of more effective catalysts. In this context, this work had as its main objective the complete elucidation of the iminium ion mechanism of conjugated addition of nitromethane to 4-phenilbut-3-en-2-one catalyzed by primary amino-thiourea (APTB) in an aprotic solvent. This system presented such mechanistic complexity, which led us to the need to investigate simpler imine formation mechanisms, how the nature of the solvent would impact it, and the effect that the presence of contaminants in the reaction medium has on the reaction. According to our results, the formation of imines in aqueous solution has the formation of a zwitterion as a rate-determining step, followed by the formation of carbinolamine catalyzed by water molecules and then, through elimination of hydroxide ion, there is the formation of iminium ions. The formation of imines and unsaturated imines in the aprotic solvent has its kinetic viability conditioned to the presence of acids as contaminants in the reaction medium, which, of the species investigated here, are the only ones capable of leading to a lowering of the free energy barriers consistent with what is experimentally observed. Understanding the formation of imines provided us a more solid basis for elucidating the mechanism via iminium ion of the Michael reaction catalyzed by APTB, which has as a rate-determining step the formation of the iminium-nitronate ion pair, followed by enantioselective step, and despite not participating in these two main steps, the presence of acetic acid is essential for the other steps to have kinetic viability for continuity, as well as to allow the catalytic cycle to complete. Finally, to design a catalyst that acts exclusively via base, we used an iminophosphorane-thiourea as a reference structure, and through targeted structural modifications, we designed a new catalyst for the Michael reaction, which allowed conversion of up to 96% at 1 day of reaction time and enantiomeric excess of 97% for S isomer.

BANKING MEMBERS:
Presidente - 1623600 - JOSEFREDO RODRIGUEZ PLIEGO JUNIOR
Interno - 1222623 - MARCELO SIQUEIRA VALLE
Externa ao Programa - 1544781 - STELLA MARIS RESENDE
Externo à Instituição - HELIO FERREIRA DOS SANTOS - UFJF
Externo à Instituição - GIOVANNI WILSON AMARANTE - UFJF