Unexpected Regiospecific Reduction of the Double Bond by NaBH₄ in 2‐(1‐Methyl/1H‐benzimidazole‐2‐yl)‐3‐aryl‐acrylonitrile

Abstract

Condensation of (1H‐benzimidazole‐2‐yl)‐acetonitrile 1 with aromatic aldehydes in 5% NaOH solution gave the corresponding 2‐(1H‐benzimidazole‐2‐yl)‐3‐aryl‐acrylonitrile 2, which on treatment with NaBH₄ in ethanol unexpectedly gave 2‐(1H‐benzimidazole‐2‐yl)‐3‐aryl‐propionitrile 3 by the regiospecific reduction of the double bond. Shaking a solution of 2 with H₂/Pd‐C in methanol also gave 3. Reaction of 2 with DMS gave the corresponding N‐methylated analogue 5, which also with NaBH₄ gave 6, once again by the regiospecific reduction of the double bond as in the case of 1‐demethylated analogue (i.e., 2).

Keywords:

• 2‐cyanomethyl benzimidazoles
• aromatic aldehydes
• NaBH₄
• regiospecific reduction
• H₂/Pd‐C
• alkylations

Acknowledgment

The authors are highly indebted to the University Grants Commission (UGC), Govternment of India, New Delhi, for financial support in the form of a major research project grant.