01711nas a2200193   4500008004100000245015800041210007000199260000800269300001600277490000700293520094900300100002301249700001701272700001701289700003101306700002701337700002201364856013101386       2017                        eng d00aEnantioselective synthesis of spiro γ-butyrolactones by N-heterocyclic carbene (NHC)-catalyzed formal [3+2] annulation of enals with 3-hydroxy oxindoles0 aEnantioselective synthesis of spiro γbutyrolactones by Nheterocy  cFEB  a2013 - 20190 v163 aThe N-heterocyclic carbene (NHC)-catalyzed enantioselective formal [3 + 2] annulation of α,β-unsaturated aldehydes with 3-hydroxy oxindoles is presented. Under oxidative conditions using the bisquinone oxidant, the reaction resulted in the synthesis of spiro γ-butyrolactones in moderate to good yields, enantioselectivity and diastereoselectivity. The reaction likely proceeds via the generation of the NHC-bound α,β-unsaturated acylazolium intermediate from enals, which was intercepted by the dioxindoles in a formal [3 + 2] pathway to form the spirocyclic compounds. However, a deeper mechanistic investigation revealed that the reaction can also proceed via the homoenolate intermediate. In this case, the dioxindole was oxidized to the corresponding isatin derivative using traces of air under basic conditions, and was intercepted with the NHC-bound homoenolate intermediate in a formal [3 + 2] pathway to afford the spiro compound.1 aMukherjee, Subrata1 aJoseph, Sumi1 aBhunia, Anup1 aGonnade, Rajesh, Ghanshyam1 aReddy, Santhi, Vardhan1 aBiju, Akkattu, T.  uhttps://library.ncl.res.in/content/enantioselective-synthesis-spiro-%CE%B3-butyrolactones-n-heterocyclic-carbene-nhc-catalyzed