Spiro-Pyrrolidine-Catalyzed Asymmetric Conjugate Addition of Hydroxylamine to Enals and 2,4-Dienals

A spiro-pyrrolidine-catalyzed tandem aza-1,4-addition/hemi-acetalization reaction was developed with excellent enantioselectivity (12 examples of >= 99% ee), and several substrates proceeded with higher ee (up to 10% increase) compared with the literature data. Particularly, an interesting and unusual aza-1,6-/oxa-1,4-addition for some substrates was also observed.