Utility of 2‐Diphenylphosphoryloxy‐1,3‐Dienes in Multicomponent Hetero‐Diels–Alder Reactions to Construct Functionalized Six‐Membered Nitrogen Heterocycles.

The utility of 2‐diphenylphosphoryloxy‐1,3‐dienes for the construction of substituted six‐membered nitrogen heterocycles is presented. These dienes undergo boron trifluoride‐promoted aza‐Diels–Alder reactions when reacted with imines or related species formed in situ using aldehydes and amine derivatives. The stability of the dienes allows this three‐component reaction to be carried out with no special precautions to eliminate water or air. Thirty‐one examples of this process are presented. The usefulness of the enol phosphate functional group is highlighted in further reactions after the cycloaddition step to generate functionalized piperidenes or pyridines. [ABSTRACT FROM AUTHOR]