Site-Selectivity of Prato Additions to C: Experimental and Theoretical Studies of a New Thermodynamic Product at the dd-[5,6]-Junction.

Three Prato monoadduct isomers were synthesized and structurally characterized by H, C NMR spectra and single-crystal X-ray diffraction, and one adduct on the dd-[5,6]-bond was found as the first example of a Prato [5,6]-adduct of C. To investigate the mechanism in the generation of this dd-[5,6]-adduct, computational studies were employed to show that it was thermodynamically obtained by sigmatropic rearrangement from the presumed initial kinetic product de-[6,6]-adduct.