Formation of a Singlet Biradical by Two-electron Oxidation of an Allene compound

Abstract

During our attempts at the synthesis of stable triplet carbenes from allene 1 bearing two acridene skeletons, we found that the oxidation of 1 gives a product of interesting properties. Allene 1 was prepared from 3-iodoanisole and 3-anisidine in 4 steps in 16% overall yield. The oxidation of 1 by aminium salts resulted in a color change of the solution (to dark purple) and afforded an unexpected species as the main product. The structure of the product was confirmed by X-ray analysis to be that of a dimer with demethylation of one of the four methoxy groups. DFT calculations indicated that the dimer has open-shell singlet biradical character. The synthesis and properties of 1 and the dimer will be discussed.