Development of HB Donor Catalysts

Abstract

Two novel hydrogen bond (HB) donor catalysts were designed and developed. By bridging the HB moiety and aryl group with an electron-withdrawing group such as, ketone or sulfone, the acidities of the N–H protons can be tuned by changing the electronic nature of the electron-withdrawing groups involved. In addition, it is anticipated that the removal of the highly nucleophilic sulfur atom in thiourea would prevent the side reactions that are sometimes problematic in thiourea-catalyzed reactions. The extents of the ability of HB donation of two novel quinazoline and benzothiadiazine-derived catalysts, prepared by using the above approach, were systematically evaluated by analytical methods. It was found that the order of HB donor ability was quinazoline < thiourea < benzothiadiazine. These catalysts were subsequently examined in two asymmetric transformations, namely Michael reactions of α,β-unsaturated imides and hydrazination reactions of 1,3-dicarbonyl compounds. The former worked best with the use of thiourea catalysts whereas the latter gave best results with quinazoline-derived catalysts, which exhibit less HB donor activity than thiourea counterparts. These results show that the strongest HB donors are not necessarily the most active or most suitable catalysts for asymmetric reactions.