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■ Synthesis of Spiro[2-cyclopentene-1,3’-imidazo[1,2-a]pyridine] Derivatives and Their Interesting Behavior in 1H-NMR Spectra in Deuteriochloroform

Takashi Abe, Akikazu Kakehi,* Hiroyuki Suga, Yukihisa Okumura, and Kennosuke Itoh

*Department of Chemistry and Material Engineering, Faculty of Engineering, Shinshu University, 4-17-1 Wakasato, Nagano 380-8553, Japan

Abstract

Ethyl 2’,3’-dihydro-2-methylthio-2’,4-dioxospiro[2-cyclopentene- 1,3’-imidazo[1,2-a]pyridine]-3-carboxylates were synthesized from the reactions of 3-[bis(methylthio)methylene]-2(3H)-imidazo[1,2-a]pyridinones with ethyl 4-chloroacetoacetate in the presence of a base. The 2-methylthio group in these spiro compounds was easily replaced with some primary and secondary amines to afford the corresponding 2-amino derivatives. Very interestingly, the proton signals of these spiro compounds in the 1H-NMR spectra in deuteriochloroform (CDCl3) changed with an increase in the sample concentration, and the analysis for the magnitude and the direction of each proton shift disclosed the conformational change of the cyclopentenone moiety in this molecule.