Heterocycles structurally influenced by a side chain. X. Effect of temperature and side chain on the imine-enamine tautomerism in the quinoxalinone and pyridopyrazinone systems

✍ Scribed by Taketsugu Seki; Yasuo Iwanami; Yoshiyuki Kuwatani; Masahiko Iyoda

• Publisher: Journal of Heterocyclic Chemistry
• Year: 1997
• Tongue: English
• Weight: 491 KB
• Volume: 34
• Category: Article
• ISSN: 0022-152X
• DOI: 10.1002/jhet.5570340312

✦ Synopsis

Abstract

3‐(1‐Benzoyl)ethyl‐1__H__‐pyrido[2,3‐b]pyrazin‐2‐one (7), 3‐(1‐ethoxycarbonyl)ethyl‐1__H__‐pyrido[2,3‐b]‐pyrazin‐2‐one (8), and 3‐(1‐benzoyl)ethyl‐1__H__‐quinoxalin‐2‐one (9) exist only in the imine form due to the steric effect of the methyl substituent. As regards the imine‐enamine tautomerism, 3‐(β‐carbonylmethylene) derivatives of 1,2‐dihydro‐4__H__‐pyrido[2,3‐b]pyrazin‐3‐one such as 12 and 15–18 gradually change from the enamine form to the imine form with elevated temperatures; however, 3‐(carbonylmethylene) derivatives of 3,4‐dihydro‐1__H__‐pyrido[2,3‐b]pyrazin‐2‐one such as 10, 19 and 20 show little temperature effect. 2‐Phenacylidene‐1,2‐dihydro‐4__H__‐pyrido[3,4‐b]pyrazin‐3‐one (21) and 3‐phenacylidene‐3,4‐dihydro‐1__H__‐pyrido[3,4‐b]pyrazin‐2‐one (22), which exist in the enamine form, show no temperature effect.