Enantioselective Vinylogous Amination of 5-Alkyl-4-nitroisoxazoles with a Dipeptide-Based Guanidinium Phase-Transfer Catalyst

An enantioSelective vinylogous aininatiori of 5-alkyl-4-nitroisoxazoles is reported. With a novel chiral dipeptidebased urea amide guanidinium as the phase-transfer catalyst, the reactions worked efficiently with NaCOAc as the base, affording valuable and challenging-tosynthesizq chiral isoxazole derivatives featuring a single stereocenter at the alpha-position in high yields and with excellent enantioselectivitieS. Theoretical studies with DFT predicted that cooperative multiple hydrogen-bonding and ion pairing interactions of a nucleophile and NaOAc with the catalyst is crucial to deprotonation by reducing their HOMO-LUMO energy gap.