β,γ-trans-selective γ-butyrolactone formation via homoenolate cross-annulation of enals and aldehydes catalyzed by sterically hindered N-heterocyclic carbene
Ryuji Kyan, Yuya Kitagawa, Ryuji Ide, Kohei Sato, Nobuyuki Mase, Tetsuo Narumi
Highly sterically hindered N-heterocyclic carbenes (NHCs), can be readily prepared from the corresponding anilines, and serve as organocatalysts in NHC-catalyzed homoenolate cross-annulation of α,β-enals and aryl aldehydes. This catalysis enables the convergent construction of β,γ-trans-disubstituted γ-butyrolactones that are an important class of molecules in synthetic and medicinal chemistry. The steric features of N-aryl substituents contribute to the selectivity and electronic ones affected the efficiency of this reaction, which proceeds with high diastereoselectivity and affords a variety of β,γ-diaryl-γ-butyrolactones in up to 91% yield with up to 1:99 dr.
