Direct access to non-aromatic 1,2,3,6-tetrahydro-1,2,3,4-tetrazines via [4 + 2] cycloaddition of α-halogeno hydrazones with azodicarboxylic acid derivatives

Abstract

Construction of non-aromatic 1,2,3,6-tetrahydro-1,2,3,4-tetrazines through [4 + 2] cycloaddition of α-halogeno hydrazones with azodicarboxylic acid derivatives.

Recent Advances in the Chemistry of Conjugated Nitrosoalkenes and Azoalkenes

“…The [4 + 2] cycloaddition reaction of 1,2-diaza-1,3-butadienes provides a simple and efficient pathway to obtain novel potentially bioactive 1,2,4-triazines and nonaromatic 1,2,3,4-tetrazines (Scheme ). , Thus, azoalkenes 121 , generated in situ from the α-bromohydrazone 120 upon treatment with base, were trapped by imines to give 2,3,4,5-tetrahydro-1,2,4-triazines 122 , regioselectively and in good yields. 1,2,3,6-Tetrahydro-1,2,3,4-tetrazines 123 were synthesized by the reaction of 1,2-diaza-1,3-butadiene 121 with azodicarboxylic acid derivatives.…”

Syntheses of Tetrahydropyridazine and Tetrahydro-1,2-diazepine Scaffolds through Cycloaddition Reactions of Azoalkenes with Enol Diazoacetates

“…Among the competing processes responsible for the low yields of 3 was TBS transfer to the reactant hydrazone amide nitrogen of 1 that occurred in competition with azoalkene formation and cycloaddition between two azoalkenes; , an excess of 1a and moderation of the addition rate was required to balance these two competing processes with the intermolecular cycloaddition of azoalkene 5 with 2 . Further screening of reaction conditions, including solvent, base, and reaction temperature, indicated that the optimal yield of 3a was obtained from the reaction carried out only in the presence of cesium carbonate at room temperature in dichloromethane (Table , entry 1). , Variation of the α-halogen (entry 2), aryl substituents (entries 1, 3–7), and the ester R 2 group (entries 8 and 9) had little influence on the yield of product 3 . The reactions of γ-methyl- and γ-phenyl-substituted enol diazoacetates also yielded the desired [4 + 2]-cyclization products but with moderate yield due to steric effects from the γ-substitutions (entries 10 and 11).…”

Strategy to Construct 1,2,3‐Triazoles by K2CO3‐Mediated [4+1] Annulation Reactions of N‐Acetyl Hydrazones with Bifunctional Amino Reagents

“…Recently, α‐halogeno hydrazones were successfully used to build N ‐containing, seven‐membered heterocyclic compounds with C, N cyclic azomethine imines, phthalazinium dicyanomethanides, or nitrones [12] . The [4+2] annulation of α‐halogeno hydrazones with olefins, [13a] azodicarboxylic acid derivatives, [13b] and other C2 synthons [13c–e] have also been explored as methods for synthesizing 1,2,3,4‐tetrazines, pyridazine, and other six‐member rings. However, studies on [4+1] annulations of α‐halogeno hydrazones are limited.…”