Silica Gel, an Effective Catalyst for the Reaction of Electron-Deficient Nitro-Olefins with Nitrogen Heterocycles

Abstract

The reaction of electron-deficient olefins with nitrogen heterocycles such as pyrrole and indole was examined in the presence of silica gel at room temperature under stirring at solvent-free conditions. It was found that silica gel is an effective catalyst for this conjugate addition. This work resulted in the formation of monosubstituted pyrroles selectively as a major product except in a few cases where disubstituted pyrroles were also formed as side products. Thus, a simple, rapid, efficient, environmentally benign, and solvent-free method was established.

Keywords:

• Conjugate addition reaction
• indole
• nitro-olefins
• pyrrole
• silica gel

ACKNOWLEDGMENTS

We are grateful to Mr. B. S. Kalshetti for IR spectra, Mrs. J. P. Choudhary for NMR spectra, and Mr. D. S. Shishupal for GC-MS. A. M. A. S. is thankful to Ministry of Higher Education in Yemen for the award of a fellowship.

Notes

Notes. Yield calculated according to the recovered starting electrophile. An asterisk (*) indicates products are mixtures of diastereomers.

Note. Yield calculated according to the recovered starting electrophile.

^a Ref. [9b].