Efficient synthesis of N-nosyl-protected 3-azabicyclo[4.3.0]nonen-8-one by an aniline- and nitrobenzene-mediated Pauson–Khand cyclization

ABSTRACT

The intramolecular Pauson–Khand cyclization in the presence of both aniline and nitrobenzene was used to improve the construction of N-nitrobenzenesulfonyl-protected 3-azabicyclo[4.3.0]nonane skeletons. We found that aniline enhanced the cyclization and that nitrobenzene prevents the concurrent reduction in this process. This combination of mediators allows for the efficient synthesis of bioactive azabicyclic nonane-type alkaloids and the use of milder deprotection conditions in the synthetic route.

GRAPHICAL ABSTRACT

KEYWORDS:

• Aromatic amine
• aza-bicyclononane
• nitrobenzenesulfonyl protecting group
• Pauson–Khand reaction

Acknowledgments

We gratefully acknowledge Professor Tsubuki and Dr. Kasai of Hoshi University, Japan, and Mr. Hirose of Hokkaido University, Japan, for their kind assistance with the mass spectrometry analyses.