摘要
Stable carbocations such as tritylium ions have been widely explored as organic Lewis acids catalysts and reagents in organic synthesis.~([1]) However, to achieve asymmetric carbocation catalysis remains elusive ever since their first identification over one century ago.~([2]) The challenges mainly come from their limited compatibility, scarcity of chiral carbocation as well as the extremely low barrier to racemization of chiral carbenium ions. We reported herein a latent concept for asymmetric carbocation catalysis. In this strategy, chiral trityl phosphate is employed as the carbocation precursor, which undergoes facile ionic dissociation upon mild external stimulation(e.g. acid, H-bonding, polar substrates) to form a catalytically active chiral ion-pair for substrate activation and chiral induction. The latent strategy provides an enabling solution to the long sought-after asymmetric carbocation catalysis as illustrated in three different enantioselective transformations.~([3])
Stable carbocations such as tritylium ions have been widely explored as organic Lewis acids catalysts and reagents in organic synthesis.~([1]) However, to achieve asymmetric carbocation catalysis remains elusive ever since their first identification over one century ago.~([2]) The challenges mainly come from their limited compatibility, scarcity of chiral carbocation as well as the extremely low barrier to racemization of chiral carbenium ions. We reported herein a latent concept for asymmetric carbocation catalysis. In this strategy, chiral trityl phosphate is employed as the carbocation precursor, which undergoes facile ionic dissociation upon mild external stimulation(e.g. acid, H-bonding, polar substrates) to form a catalytically active chiral ion-pair for substrate activation and chiral induction. The latent strategy provides an enabling solution to the long sought-after asymmetric carbocation catalysis as illustrated in three different enantioselective transformations.~([3])
引文
[1]a)Mukaiyama,T.;Kobayashi,S.;Murakami,M.Chem.Lett.1984,1759-1762.b)Bah,J.;Franzén,J.Chem.Eur.J.2014,20,1066-1072.
[2]Chen,C.-T.;Chao,S.-D.;Yen,K.-C.;Chen,C.-H.;Chou,I.-C.;Hon,S.-W.J.Am.Chem.Soc.1997,119,11341-11342.
[3]Lv,J.;Zhang,Q.;Zhong,X.;Luo,S.J.Am.Chem.Soc.2015,137,15576-15583.
