Hantzsch Ester Anion as Electron Donor in Transition-Metal-Free Photoinducided N-Desulfonylation Reactions

MICAELA D. HEREDIA; WALTER D. GUERRA; MARÍA E. BUDÉN; SILVIA M. BAROLO; ROBERTO A. ROSSI

Viña del Mar

Congreso; ELAFOT XIV; 2019

Hantzsch esters (HEs) have been used as reductants in catalytic hydrogenation reactions. Recently, with the advances in the visible light photoredox catalysis, it has been grown the use of HEs as electron donors and proton sources in many photoredox reaction types. For example, in hydrodifluoroalkylation of alkenes, reductive couplings of carbonyls with alkenes or carboxylation of aromatic and aliphatic bromides and triflates.Sulfonyl group is useful for protecting nitrogen containing compounds. However, due to its great stability, requires rigorous deprotection conditions. Recently, it has been developed a photocatalytic N-S cleavage using an iridium complex and the HE to give amides as products in excellent yields.Here, we report an efficient and transition-metal-free photoinducided desulfonylation method using the Hantzsch ester anion as promotor. The photostimulated reaction (visible light) of methyl aryl sulfonamide, in the presence of HE anion (2 equiv.) in DMSO for 1 hour afforded the deprotected product (methyl aniline) in 92 % yield at room temperature. There was not reaction under dark conditions, which excludes a polar mechanism. The effect of the base was evaluated by carrying out the photostimulated reaction in the absence of KOtBu. Under this condition the product methyl aniline was not obtained indicating that the base is necessary. Also, the reaction without HE only in presence of KOtBu (or NaH) gave the product in 15% yield. This result indicates that HE anion is responsible to initiate the ET reaction.