Banca de QUALIFICAÇÃO: ROBERTA ALBINO DOS REIS

Uma banca de QUALIFICAÇÃO de DOUTORADO foi cadastrada pelo programa.
DISCENTE : ROBERTA ALBINO DOS REIS
DATA : 13/12/2021
HORA: 13:30
LOCAL: meet.google.com/rck-zrdu-hus
TÍTULO:

Use of fluorescent oxalate esters to observe the nucleophilic nature of the sterically hindered DBU

PÁGINAS: 27
RESUMO:

The organic base 1,8-diazabicyclo[5.4.0]undec-7-ene (DBU) is a well-known catalyst, used in many chemical transformations. DBU was formerly considered a non-nucleophilic base due to its steric hindrance, nonetheless, it can also act as a nucleophilic species in esterifications and reacting with Michael acceptors. At this study, we have acquired clear-cut evidence that DBU can act as a nucleophilic species towards the decomposition of fluorescent oxalate esters. First, we synthesized a series of five lophine derivatives, containing a hydroxyl group at the 2-phenyl ring and different substituents (H, Br, F, CH₃, OCH₃) at the 4 and 5-phenyl. These all presented fluorescence quantum yields above 10%, apart from Br (ca. 1.2%). The lophines with H and Br groups were reacted with oxalyl chloride to prepare two oxalate esters, respectively, O1 and O2. Using kinetic data obtained from fluorescence and absorption measurements, we observed that O1 reaction with DBU follows a sequential process, with two addition/elimination reactions via B_AC2 occurring with DBU acting as a nucleophile. The first B_AC2 transformation in this sequence has a bimolecular rate constant 20 times faster than the second one. Also, our photophysical data suggests that ionic pairs are generated as reaction intermediates, after the elimination of the leaving group. For ester O2, bearing a better leaving group, the observed bimolecular rate constant for its reaction with DBU is comparable to the one of reactive electrophilic Michael acceptors. Therefore, DBU is an efficient nucleophilic catalyst for the decomposition of oxalate esters.

MEMBROS DA BANCA:
Presidente - Interno ao Programa - 1939561 - FERNANDO HEERING BARTOLONI
Membro Titular - Examinador(a) Interno ao Programa - 1544394 - PAULA HOMEM DE MELLO
Membro Titular - Examinador(a) Interno ao Programa - 1909951 - ARTUR FRANZ KEPPLER
Membro Suplente - Examinador(a) Interno ao Programa - 1544379 - ANDERSON ORZARI RIBEIRO