Aerobic Oxidation/Annulation Cascades through Synergistic Catalysis of RuCl3 and N-Heterocyclic Carbenes

Qian Wang; Jiean Chen; Yong Huang

doi:10.1002/chem.201803254

Aerobic Oxidation/Annulation Cascades through Synergistic Catalysis of RuCl₃ and N-Heterocyclic Carbenes

Chemistry. 2018 Sep 3;24(49):12806-12810. doi: 10.1002/chem.201803254. Epub 2018 Aug 2.

Authors

Qian Wang¹, Jiean Chen¹, Yong Huang¹

Affiliation

¹ State Key Laboratory of Chemical Oncogenomics, Key Laboratory of Chemical Genomics, Peking University, Shenzhen Graduate School, Shenzhen, 518055, P. R. China.

PMID: 29978509
DOI: 10.1002/chem.201803254

Abstract

Cooperative catalysis combining a transition metal with an N-heterocyclic carbene is challenging due to strong binding of NHCs towards late transition metals. We report the first example of synergistic catalysis by a chiral NHC and a coordinatively unsaturated ruthenium compound. RuCl₃ was found to mediate efficient aerobic oxidation of homoenolates generated from enals and the N-heterocyclic carbene. The resulting α,β-unsaturated acylazolium intermediate reacts selectively with 1,3-dicarbonyl compounds or ketones at either the β- or γ-carbon, yielding polysubstituted chiral lactones in high yield and with excellent enantioselectivity (up to 98 % yield, 94 % ee). This protocol can be applied to structurally sophisticated substrates.

Keywords: N-heterocyclic carbenes; cooperative effects; oxidation; ruthenium; synergistic catalysis.