Fig. 4. EPR spectroscopic studies.

a Experiments illustrating the dual role of KOt-Bu. b EPR spectra (X-band, 295 K) of samples from the reaction of 1a with KOt-Bu (reaction I; solid black line), from the two-step reaction of 1a with KOt-Bu and then with 2a (reaction II; solid blue line), and from the two-step reaction of 1a with KOt-Bu and then with 2a and LiOt-Bu (reaction III; solid red line). c EPR spectra (X-band, 295 K) of samples from the reaction of 1a with KOt-Bu (reaction I; dotted black line) and from the annulation of 1a with KOt-Bu and 2a (solid red line), with sample transfer conducted in an Ar atmosphere in both cases. The spectrum of the annulation was acquired using a microwave power one hundred times that used for the spectrum of the 1a–KOt-Bu reaction.