5‐Substituted 4,5‐Dihydro‐1,2,4‐triazin‐3(2H)‐ones from the Unprecedented Reaction between α‐N‐Protected Amino Acid Hydrazides and NaBH₄

Abstract

α‐N‐Protected amino acid hydrazides (1) readily reacted with NaBH4 to afford 5‐substituted 4,5‐dihydro‐1,2,4‐triazin‐3(2H)‐one derivatives 2 in good yields. Unfortunately, the reaction caused partial racemization at the α‐amino acidic carbon atom of the starting hydrazide. A mechanism, supported by experimental evidence, has been proposed in an attempt to explain this to date unprecedented reaction. The structure of compounds 2 was confirmed by X‐ray structural analysis. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2006)