Combined Computational and Experimental Study on [5 + 2] Cycloaddition of 2-Trifluoromethylated Oxidopyrylium Species Leading to 1-(Trifluoromethyl)-8-oxabicyclo[3.2.1]oct-3-en-2-ones.

Trifluoromethylation of furfural using the Ruppert-Prakash reagent (TMSCF3) and subsequent photo-Achmatowicz reaction afforded 6-hydroxy-2-(trifluoromethyl)-2H-pyran-3(6H)-one. After acetylation, the resultant 6-acetoxy-2-(trifluoromethyl)-2H-pyran-3(6H)-one was transformed into various 1-(trifluoromethyl)-8-oxabicyclo[3.2.1]oct-3-en-2-one derivatives through a base-mediated oxidopyrylium [5 + 2] cycloaddition. The reactivity and selectivity of the 2-trifluoromethylated oxidopyrylium species toward [5 + 2] cycloaddition were analyzed using density functional theory calculations.