Asymmetric Syntheses of Nitroso Diels-Alder-Type Bicycloketones

Significance

Organocatalytic asymmetric syntheses of nitroso Diels-Alder-type bicycloketones using aromatic nitroso compounds 3 and preformed (1) or in situ generated dienamines derived from α,β-unsaturated ketones 2 are described. 2-Oxa-3-aza-bicycloketones 4 are obtained in good yields and high enantioselectivities in the presence of chiral BINOL 5. Mechanistic investigations based on experimental data revealed that the reaction proceeds via an N-nitroso aldol reaction followed by a Michael addition. Chiral pyrro­lidine 7 provides 3-oxa-2-aza-bicycloketones 6 in moderate yields and excellent enantioselectivities. Remarkably, both cyclizations show perfect regio­selectivities. In addition, 3-oxa-2-aza-bicyclo-ketones 6 can be transformed into enantiopure 1-amino-3,4-diols 8.