Au nanoparticlessupported on TiO2 (1 mol %) catalyze the quantitative cycloisomerization of conjugated allenones into furans under very mild conditions. The reaction rate is accelerated by adding acetic acid (1 equiv), but the acid does not participate in the protodeauration step as in the corresponding Au(III)-catalyzed transformation. The process is purely heterogeneous, allowing thus the recycling
to substituted 3‐keto pyridines or 4‐picolines in very good yields. This pathway is in contrast to their known cyclization in the presence of Au(I) or Au(III) catalysts which provides 1,4‐oxazepines, instead. The enaminones are formed in situ upon mixing a conjugated allenone or allenyl ester with the alkynylamine, thus the pyridine‐forming transformation is typically a onepot process.
TiO 2上的可回收负载型Au纳米颗粒催化N-炔丙基或N-同炔丙基β-烯胺酮的环化,然后进行脱氢(芳构化),从而以非常好的收率产生取代的3-酮吡啶或4-甲基吡啶。该途径与已知在Au(I)或Au(III)催化剂存在下环化的相反,后者提供1,4-氧杂氮杂pine。烯胺酮是在将共轭的Allenone或Allenyl酯与炔基胺混合后原位形成的,因此形成吡啶的转化通常是一锅法。
Asymmetric Aza-Claisen Rearrangement between Enantioenriched α-Chiral Allylamines and Allenones
An unprecedented asymmetric aza-Claisen rearrangement between enantioenriched α-chiral allylamines and allenones was found to proceed in the absence of catalysts and additives at room temperature. The rearrangement, followed by hydrolysis, provides convenient access to structurally diverse δ-chiral β-diketones in good to excellent yields with excellent retention of enantiopurity. This protocol proved