Chiral Pyrrolidine Bridged Polyhedral Oligomeric Silsesquioxanes as Heterogeneous Catalysts for Asymmetric Michael Additions
A chiral pyrrolidine bridged polyhedral oligomeric silsesquioxane (SQ) was synthesized, characterized, and used as an effective heterogeneous catalyst. The synthesis involves two simple steps: nucleophilic substitution between benzylchloride functionalized SQ and imidazoyl pyrrolidine carboxylate and subsequent deprotection. The catalyst was isolated by simple filtration. The SQ-supported chiral pyrrolidine catalyst was used as a heterogeneous catalyst in an asymmetric Michael addition into nitrostyrenes under room temperature and neat condition, giving the product in excellent yields (85–91%), diastereoselectivities (up to 99:1) and enantioselectivities (95–98%). The catalyst can be recycled by a simple filtration without a significant loss in its reactivity and selectivity.
KeywordsSilsesquioxane POSS Asymmetric catalysis Michael reaction Heterogeneous catalysis
This research was supported by Thailand Research Fund (MRG5980118 for T.L.), the Central Instrument Facility, the Faculty of Science, Mahidol University, and the Center of Excellence for Innovation in Chemistry (PERCH-CIC), Office of the Higher Education Commision (OHEC), Ministry of Education. S.H. thanks a graduate student financial support from TRF IRG5980007.
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