Synthesis of N,N-Bis(nonaflyl) Squaric Acid Diamide and its Application to Organic Reactions

摘要

Bransted acid catalysis is one of the growing fields in modern organic synthesis. Although several Bransted acids, such as urea/thiourea, TADDOL, and phosphoric acid, have been applied to a variety of organic reactions, other Bronsted acid scaffolds have been much less explored. Recently, Rawal et al have developed a Bronsted acid catalyst based on squaric acid moiety and successfully applied it as a catalyst for conjugate addition of 1,3-dicarbonyl compounds to nitroolefins. More recently, we have developed a strong Bronsted acid derived from squaric acid by introducing a strong electron withdrawing tri-fluoromethanesulfonyl (Tf) group and applied it to Mukaiyama aldol and Michael reaction of a yariety of aldehydes, ketones, and α,β-unsaturated ketones. As a continuing effort to develop strong Bronsted acids based on the squaric acid scaffold, it was expected that replacement of Tf group with a longer perffuoro-alkanesulfonyl group would be able to tune the physical properties, such as solubilities in organic solvents and fluoro-philicity, without loss of reactivity (Figure 1). Herein, we report the development of a new Bronsted acid based on the squaric acid scaffold carrying two nonafluorobutanesulfonyl (Nf) groups and the preliminary results of its reactivity to various organic reactions.