The fluoride promoted vinylogous Mukaiyama-Michael reaction (VMMR) of 2-trimethylsilyloxyfuran with diverse α,β-unsaturated ketones is described. The TBAF catalyzed VMMR afforded high anti-diastereoselectivity irrespective of the solvents used. The KF/crown ethers catalytic systems proved to be highly efficient in terms of yields and resulted in a highly diastereoselective unprecedented solvent/catalyst switchable reaction. Anti-adducts were obtained as single diastereomers or with excellent diastereoselectivities when benzo-15-crown-5 in CH2Cl2 was employed. On the other hand, high syn-diastereoselectivities (from 76:24 to 96:4) were achieved by employing dicyclohexane-18-crown-6 in toluene. Based on DFT calculations, the catalysts/solvents-dependent switchable diastereoselectivities are proposed to be the result of loose or tight cation-dienolate ion pairs.
Bibliographical noteKAUST Repository Item: Exported on 2020-10-01
Acknowledgements: Financial support from the University of Salerno (FARB) and Regione Campania under POR Campania FESR 2007-2013 – O.O. 2.1 (Farma-BioNet). We thank Dr. Patrizia Iannece for HRMS. Gilles Hanquet and Frédéric Leroux thank the CNRS (Centre National de la Recherche Scientifique, France). Chloé Batisse is very grateful to the IcFRC (International Center for Frontier Research in Chemistry), grant Cyclo-CF2-ASYM. Luigi Cavallo thanks the King Abdullah University of Science and technology for supporting this work. Computing resources used within this project have been provided by the KAUST Supercomputing Laboratory and by CRESCO/ENEAGRID High Performance Computing infrastructure and its staff.