A Novel Synthetic Method of Bicyclic Pyrans via the Palladium-Catalyzed Tandem­ Cyclization/Ring Expansion between Enynals and Dimethyl Acetyl­enedicarboxylate

Abstract

The reaction of enynals 1 with dimethyl acetylenedicarboxylate 2 in the presence of Pd(OAc)₂ and COD (cyclooctadiene) gives the bicyclic pyrans 3 in good yields.

Key words

bicyclic pyran - tandem reaction - cyclization - ring expansion - palladium catalyst

References

• For reviews, see:
• 1a Kantorowski EJ. Kurth MJ. Tetrahedron  2000,  56:  4317 
• 1b Roxburgh CJ. Tetrahedron  1993,  47:  10749 
• 2 Asao N. Nogami T. Lee S. Yamamoto Y. J. Am. Chem. Soc.  2003,  125:  10921 
• 3a Asao N. Nogami T. Takahashi K. Yamamoto Y. J. Am. Chem. Soc.  2002,  124:  764 
• 3b Mondal S. Nogami T. Asao N. Yamamoto Y. J. Org. Chem.  2003,  68:  9496 

4

Although we attempted to observe the formation of 6 in the reaction of 1a with Pd catalyst in the absence of 2, we could not detect it, probably due to very low stability of 6 under the reaction conditions mentioned above.