Sustainable synthesis of vinyl sulfones using copper catalysis

Allenes are a class of compounds with two cumulated carbon-carbon double bonds, which are versatile synthetic intermediates in organic synthesis. They have shown an interesting reactivity and selectivity affording complex structures in a limited number of steps using a wide variety of transition metals. On the other hand, sulfonyl derivatives are very important compounds as they can be found in sulfones and sulfonamides, two classes of compounds with prominent biological and pharmacological activities. Our research group has reported a gold(I)-catalyzed cyclization of allenic carbamates to obtain 1,3-oxazinan-2-ones. In this context, we decide to study a copper-catalyzed cascade heterocyclization/sulfonylation for the controlled preparation of sulfonyl oxazinanones. Surprisingly, in this work we have isolated a great variety of vinyl sulfones with high selectivity instead of the desired cyclization . These sulfones are obtained by the reaction between N-Boc-allenes and aromatic sodium sulfinates. The reaction is carried out at 100 ºC in a sealed tube, where copper acetate (II) is employed as the catalyst and silver nitrate as the oxidant. Both electron-donating and electron-withdrawing groups are tolerated on the aromatic rings of the carbamates and sodium sulfinates. We were able to control the reactivity of allenes toward the formation of bis(γ-amino-functionalized vinyl sulfones) in the presence of copper salts under radical conditions.