Azomethine Ylide Cycloaddition Approach toward Dendrobine: Synthesis of 5-Deoxymubironine C.

A concise route to the azatricyclo[6.2.1.04,11]undecane core of (-)-dendrobine and (-)-mubironine C is described wherein an unstabilized azomethine ylide cycloaddition provides the complete carbon framework of the natural products. The cyclization precursor is made in short order from ( R)-carvone through an unconventional high-pressure Ireland-Claisen reaction. Attempts to install a final hydroxyl group through an intramolecular lactonization strategy and the observation of an unexpected and highly complex enal-ene product are also reported.