Esters are for the first time used as α,β-unsaturated alkynyl acyl ammonium and azolium precursors to undergo a formal [2 + 3] annulation with amidomalonates through DMAP/LiCl or carbene/LiCl cooperative catalysis. A wide range of (Z)-5-amino-3-furanones were obtained in moderate to high yields with high regioselectivity and stereoselectivity. In addition, a plausible mechanism based on the calculated charge distribution of the intermediates is proposed to explain the regioselectivity.
A stereoselective synthetic approach to spirooxindole γ-butyrolactams is developed via N-heterocyclic carbene-catalyzed formal [3 + 2] annulation of α-bromoenals with 3-aminooxindoles. An enantioselective variant of this methodology is also investigated resulting in good substrate tolerance and high enantioselectivities.
Alkynyl acylammoniums generated in situ from alkynyl acids are first used as electrophilic 3C synthons in a formal [3 + 3] annulation with 1,3-dicarbonyl compounds for regioselective synthesis of functionalized 4H-pyran-4-ones via a 4-(dimethylamino)pyridine/Lewis acid dual-activation strategy. This protocol paves the way for further investigation of alkynyl acylammoniums as 3C synthons for construction of diverse heterocyclic skeletons.
β-Functionalization of indolin-2-one-derived aliphatic acids has been applied in formal [3 + 2] annualtions for catalyst-free and divergent synthesis of two series of structurally interesting 3,3'-spirooxindole γ-butyrolactones that may be attractive for potential drug discovery. These findings also pave the way for further diversity-oriented synthesis of spirooxindoles starting from indolin-2-one-derived aliphatic acids or their derivatives.
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