The first catalytic inverse-electron demand hetero-Diels-Alder reaction of nitroso alkenes using pyrrolidine as an organocatalyst |
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Authors: | Wabnitz Tobias C Saaby Steen Jørgensen Karl Anker |
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Institution: | The Danish National Research Foundation: Center for Catalysis, Department of Chemistry, Aarhus University, 8000 Aarhus C, Denmark. |
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Abstract: | The first catalytic inverse-electron demand hetero-Diels-Alder reaction of nitroso alkenes has been developed. Nitroso alkenes were generated in situ from alpha-halooximes and underwent 4 + 2]-cycloadditions with enamines as dienophiles formed from aldehydes and pyrrolidine (10 mol%) as an organocatalyst. The presence of a suitable heterogeneous buffer system was found to be essential and best results were obtained with sodium acetate trihydrate. The resulting 5,6-dihydro-4H-oxazines were obtained in moderate to good yields under mild reaction conditions. A catalytic cycle has been proposed and evidence for the cycloaddition mechanism has been obtained. Moderate asymmetric induction (42% ee) was observed when a chiral secondary amine was used. |
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