N-Heterocyclic Carbene Catalyzed Reaction of Enals and 1,2-Dicarbonyl Compounds:  Stereoselective Synthesis of Spiro γ-Butyrolactones

Abstract

[reaction: see text]. Nucleophilic heterocyclic carbene (NHC) catalyzed annulation of enals and cyclic 1,2-dicarbonyl compounds, opening a route to gamma-spirolactones, has been observed for the first time. The strategy works well with isatins, leading to spiroannulated oxindole derivatives. It is conceivable that the spiroannulation protocol reported herein will be applicable to the synthesis of important natural products that are endowed with a spiro gamma-butyrolactone motif, especially oxindoles and norsesquiterpenoids.

Organocatalytic Reactions Enabled by N-Heterocyclic Carbenes

“…146 Cyclohexanedione 61 and isatins 62 are competent electrophiles for this process, as well as electron-rich or electron-deficient enals. Yields for the spiro-cyclohexanone products range from 60–74% while spiro-oxindole γ-lactones are formed in 85–98% yield.…”

A Fluorous, Pummerer Cyclative‐Capture Strategy for the Synthesis of N‐Heterocycles

“…5-Bromo-1-propyl-1H-indol-2,3-dione (20) [35] from 19: TFAA (0.030 mL, 0.216 mmol, 2 equiv) was added to a solution of 19 (0.081 g, 0.108 mmol, 1 equiv) in THF (2 mL) at 0 8C and the reaction was stirred at 0 8C for 2.5 h. NEt 3 (1.5 mL, 0.011 mmol, 0.1 equiv) and ethanol (0.010 mL, 0.238 mmol, 2.2 equiv) were then added to the reaction at 0 8C and the reaction was stirred at room temperature for 4.5 h. After this time, the www.chemeurj.org reaction mixture was quenched with aqueous saturated NaHCO 3 (10 mL) and the aqueous layer extracted with CH 2 Cl 2 (3 15 mL). The organic layer was then washed with aqueous saturated NaHCO 3 (2 10 mL), dried (MgSO 4 ), filtered and concentrated in vacuo to give the crude product.…”

Synthesis of 3‐Alkylcoumarins from Salicylaldehydes and α,β‐Unsaturated Aldehydes Utilizing Nucleophilic Carbenes: A New Umpoled Domino Reaction

“…The generation of homoenolate equivalents, by NHC-catalyzed Umpolung of α,β-unsaturated aldehydes, was independently described by Glorius [6] and Bode [7] in the synthesis of γ-butyrolactones. Subsequently, this methodology has been extended towards the synthesis of β-lactones, [8] spiro γ-butyrolactones, [9] γ-lactams [10] and to redox esterification of α,β-unsaturated alScheme 1. Reaction path a: synthesis of 2,2-dimethyl-2H-chromene-3-carbaldehydes 3 and 9-methyl-8,12-dioxatricyclo[7.3.1.0 2,7 ]trideca-2,4,6-trien-11-ols 4.…”