Figure 2. The optimized transitions states of the 3,4- and 3,5- disubstituted isoxazoles generated from B3LYP/6-31G+(d) calculations in the gas phase

From

Solvent Effects on the [3+2] Cycloaddition of 2-Furfural Oxime and Ethyl Propiolate: Unexpected Change in Regioselectivity

Promi Rahman, Amy Glanzer, Jaffarguriqbal Singh, Nanette M. Wachter, Jonathan Rhoad, Richard W. Denton

World Journal of Organic Chemistry. 2017, 5(1), 6-10 doi:10.12691/wjoc-5-1-2