Efficient Enantioselective Synthesis of Dihydropyrans Using a Chiral N,N′-Dioxide as Organocatalyst
摘要:
The bifunctional organocatalyst C3 N,N'-dioxide has been successfully applied to the asymmetric cascade Michael/hemiacetalization reaction of alpha-substituted cyano ketones and beta,gamma-unsaturated alpha-ketoesters for the synthesis of multifunctionalized chiral dihydropyrans. The corresponding products were obtained in excellent yields (up to 99%) with high to excellent enantioselectivities (up to 99% ee).
Unexpected Cascade Reactions of
<i>Ortho</i>
‐Hydroxyenaminones and β,γ‐Unsaturated α‐Ketoesters to Access Hydrogenated Benzoxazolepolycycles and Pyrrole−Phenol Atropisomers
作者:Xuguan Bai、Lele Wang、Ziying Zhang、Kuan Zhang、Zhanwei Bu、Yufeng Wu、Wenjing Zhang、Qilin Wang
DOI:10.1002/adsc.201900950
日期:2019.11.5
BF3 ⋅ OEt2‐catalyzed Michael addition/cyclization/dehydration sequence of ortho‐hydroxyenaminones with aromatic or aliphatic aldehyde‐derived β,γ‐unsaturated α‐ketoesters has been achieved to afford a wide range of fused hydrogenated benzoxazole polycycles in 67–95% yields in a highlydiastereoselective manner. When isatin‐derived β,γ‐unsaturated α‐ketoesters were employed as substrates, completely different reactivities
AbstractA highly effective aldol cyclization of α‐isothiocyanato imide to both β,γ‐unsaturated α‐keto esters and aryl‐substituted α‐keto esters has been developed. A chiral N,N′‐dioxide–yttrium triflate complex was used as the catalyst. A series of cyclic thiocarbamates bearing chiral quaternary stereocenters was synthesized in good to high yields, excellent diastereo‐ (up to 25:1 dr) and enantioselectivities (up to 99 % ee). In addition, the reaction could be carried out on a gram‐scale, and other functionalized derivatives are also conveniently transformed. Interestingly, a discrepancy of diastereoselection was observed between the reactions of β,γ‐unsaturated α‐keto esters and aryl‐substituted α‐keto esters. Moreover, a substrate dependency of non‐linear effects was observed in this reaction. On the basis of the experimental results and the absolute configuration of the products, possible catalytic models have been proposed to explain the origin of the asymmetric process.magnified image