Synthesis of Novel Crown Ether-Squaramides and Their Application as Phase-Transfer Catalysts
Open Access
Abstract
This work presents the synthesis of six new phase-transfer organocatalysts in which the squaramide unit is directly linked to the nitrogen atom of an aza-crown ether. Four chiral skeletons, namely hydroquinine, quinine, cinchonine (cinchonas), and α-d-glucopyranoside were responsible for the asymmetric construction of an all-carbon quaternary stereogenic center in α-alkylation and Michael addition reactions of malonic esters. We investigated the effects of these different chiral units and that of crown ethers with different sizes on catalytic activity and enantioselectivity. During extensive parameter investigations, both conventional and emerging green solvents were screened, providing valuable α,α-disubstituted malonic ester derivatives with excellent yields (up to 98%).Keywords
Funding Information
- Hungarian Scientific Research Fund (FK138037, K128473)
- Magyar Tudományos Akadémia (János Bolyai scholarhip of Jozsef Kupai)
- Emberi Eroforrások Minisztériuma (ÚNKP-20-3-II-BME-325, ÚNKP-21-2-I-BME-209, ÚNKP-20-5-BME-322)
- Gedeon Richter (Talentum PhD Scholarship of Zsuzsanna Feher)
- Servier (France) (PhD Scholarship of Sandor Nagy)
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