Simple Synthesis of 7‐Formyl‐indole

Abstract

A simple route to 7‐formyl‐indole (5) is described in which appropriately functionalized o‐nitrotoluenes (1) are converted to 7‐hydroxymethyl‐indole (4) using the Batcho–Leimgruber process. Condensation of 3‐methyl‐2‐nitrobenzyl alcohol (1a) with N,N‐dimethylformamide dimethyl acetal yields the enamine 2a, which upon catalytic hydrogenation affords 4 in 22% yield. When the hydroxyl function in 1 is protected with pivaloyl or tetrahydropyranyl group, the yields of 4 are increased to 39% and 48%, respectively. Finally, 4 is oxidized with pyridinium chlorochromate (PCC) to afford 5 in 86% yield.

Dedicated to Professors H. Junjappa and H. Ila in recognition of their contribution to organosulfur chemistry.

Keywords:

• Batcho–Leimgruber reaction
• benzyltriethylammonium borohydride
• 7‐formyl‐indole
• 7‐hydroxymethyl‐indole
• pyridinium chlorochromate

Acknowledgments

The authors gratefully acknowledge the support from Glenmark Research Centre. The authors thank B. Gopalan for stimulating discussions and suggestions on the subject. The authors also thank Nauzer P. Dubash and Naveen Kumar Mangu for providing technical help.

Notes

Dedicated to Professors H. Junjappa and H. Ila in recognition of their contribution to organosulfur chemistry.