title: Bifunctional N-heterocyclic carbene catalyzed [3+4] annulation of enals and aurones.
abstract: Bifunctional N-heterocyclic carbenes with a free hydroxy group are demonstrated as efficient catalysts for the [3+4] annulation of enals with aurones to give the corresponding benzofuran-fused ε-lactones in good yields with good diastereoselectivities and excellent enantioselectivities. Control experiments reveal that the [3+4] cycloadducts are kinetically favored and could be transformed to the thermodynamically favored [3+2] cycloadducts with a non-bifunctional NHC catalyst.
authors.affiliation: Beijing National Laboratory for Molecular Sciences, CAS Key Laboratory of Molecular Recognition and Function, Institute of Chemistry, Chinese Academy of Sciences, Beijing 100190 (P. R. China), Fax: (+86) 10-62554449.
authors.forename: Zhi-Qin
authors.initials: ZQ
authors.lastname: Liang
authors.forename: Zhong-Hua
authors.initials: ZH
authors.lastname: Gao
authors.forename: Wen-Qiang
authors.initials: WQ
authors.lastname: Jia
authors.forename: Song
authors.initials: S
authors.lastname: Ye
keywords: N-heterocyclic carbenes; annulation; kinetic control; lactones; organocatalysis