Different modes of acid-catalyzed cyclization of 4-(γ-oxoalkyl)semicarbazide hydrazones: 7-membered versus 14-membered cyclic semicarbazones formation

Add time:08/08/2019    Source:sciencedirect.com

Acid-catalyzed cyclization of 4-(γ-oxoalkyl)semicarbazide hydrazones has been studied. 7-Membered cyclic semicarbazones, 2,4,5,6-tetrahydro-3H-1,2,4-triazepin-3-ones, were obtained from the γ-phenyl-substituted semicarbazides, while the cyclization of the γ-methyl-substituted semicarbazides involved two molecules of the starting material to result in 14-membered cyclic bis-semicarbazones, 1,2,4,8,9,11-hexaazacyclotetradeca-7,14-diene-3,10-diones. The 4-(γ-oxoalkyl)semicarbazide hydrazones were prepared according to a four-step synthesis based on amidoalkylation of the sodium enolates of 1,3-diketones with ethyl N-(1-tosylalk-1-yl)carbamates followed by base-promoted retro-Claisen reaction and treatment of the obtained ethyl N-(γ-oxoalkyl)carbamates with hydrazine.

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