Chiral Pentacarboxycyclopentadienebased Br(?)nsted Acidcatalyzedenantioselective Protonation Of Silyl Enol Ethers

The asymmetric protonation of prochiral enolate compounds is a straightforward way for the preparation of optically active a substituted carbonyl compounds.Compared with Lewis acid,the commonly Br(?)nsted acid,chiral phosphoric acid,is weakly acidic,so only a few examples have been reported.We have found a chiral PCCP catalyst prepared by(-)-borneol,which successfully achieved the asymmetric protonation reaction of silyl enol ether by using water as a proton source.Up to 99%yield and 75%ee of the product were obtained for this reaction,and better substrate suitability for the a-aromatically substituted cyclic compound were obtained too.In addition,PCCP also works well in the asymmetric ring-opening reaction of mesogenic epoxy with up to 99%yield and 81%ee.The catalyst works ordinary in the asymmetric amination reaction of cyclic carbonyl a-position by sulfur.Although up to 71%yield was obtained,less than 10%was obtained too,and further optimization of the reaction conditions is required.Compared with ordinary organocatalysis,chiral PCCP catalyst is more acidic,cheaper,and more convenient to synthesize,which shows that this catalyst has a bright prospect.