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Paper | Regular issue | Vol 87, No. 2, 2013, pp.319-328
Published online, 21st December, 2012
DOI: 10.3987/COM-12-12623
Role of CH/O and CH/π Interactions in Structural Stability. Effect on Endo Selectivity in 1,3-Dipolar Reaction of Electron-Deficient 4-Oxo-4H-pyrazole 1,2-Dioxide with N-Substituted Maleimides

Koki Yamaguchi, Kazunobu Harano, and Masashi Eto*

*Faculty of Pharmaceutical Sciences, Sojo University, 4-22-1, Ikeda, Kumamoto-shi, 860-0082, Japan

Abstract

The molecular structure of the 1:2 cycloadduct derived from 1,3-dipolar reaction of 3,5-bis(methoxycarbonyl)-4-oxo-4H-pyrazole 1,2-dioxide (1a) with N-phenyl maleimide (2a) was established to be an anti-endo-endo form by the single crystal X-ray analysis. The weak attractive CH/O interaction between 1a and 2a is conjectured to play an important role in the preferential formation of the endo transition-state. The formation mechanism of the adduct is discussed on the basis of transition-state structures optimized at the B3LYP/6-31G(d) level of theory.