Total Synthesis of 7-Hydroxymurrayazolinine, Murrayamine D, and Mahanine via m-Nitro Group Activated Pyran Annulation

The facile total synthesis of the natural product (+/-)-mahanine was obtained in eight steps with an overall 52% yield from readily accessible known nitrophenol derivative 6. After a one-step, acid-catalyzed annulation, two additional natural products were formed including 7-hydroxymurrayazolinine, representing its first reported total synthesis. In the whole process, the introduction of the m-nitro group significantly enhanced the key pyran annulation reaction through inductive effects.