Facile Synthesis of 2,3,6,11-Tetrahydro-1H,5H-indolizino[8,7-b]indole-11b-Carboxylic Acid Methyl Ester via a 9-BBN-Mediated Tertiary Lactam Reduction

Abstract

A facile synthesis of 2,3,6,11-tetrahydro-1H,5H-indolizino[8,7-b]indole-11b-carboxylic acid methyl ester, a versatile intermediate utilized in the synthesis of indole alkaloids, was achieved in two steps. Condensation of tryptamine with dimethyl α-ketoglutarate led to the formation of the corresponding indolizino[8,7-b]indolone ester, which subsequently underwent an efficient lactam reduction with 9-BBN to generate the tertiary amine ester in good yield.

Keywords:

• 9-BBN
• Dimethyl α-ketoglutarate
• lactam reduction
• tryptamine

ACKNOWLEDGMENTS

The authors thank ArQule's Analytical Department for the mass spectra analysis of the compounds described in the article.