NHC-Catalyzed Cascade Reaction between β-Methyl Enals and Dienones for Quick Construction of Complex Multicyclic Lactones

Abstract

Scheme 4. Scope of Enals 1 and Pyranone Dienones 7 a a Yields are isolated yields after purification by column chromatography. dr values were determined by 1 H NMR on the crude reaction mixture. er values were determined via HPLC on the chiral stationary phase. The absolute configuration of 8b was determined via X-ray analysis of its single crystals.

Synthesis and Reactivity of Electron-Deficient 3-Vinylchromones

“…A cascade reaction between chromones 5 and β-methylacroleins under the action of N-heterocyclic carbene (NHC catalysis) has been described, 84 which provides a rapid approach to tetracyclic lactones 169 with a quaternary chiral carbon center (Scheme 65). To implement this diastereo-and enantioselective transformation, tetracyclic triazolium NHC 167 was used as a catalyst, quinone 168 as an oxidizing agent, and AcONa as a base.…”

“…The resulting adduct 171 undergoes Michael cyclization to intermediate 172, the lactonization of which gives the final product 169. 84,85 Scheme 65 Synthesis of compounds 169 and mechanism their formation…”

“…For example, chiral α,β-unsaturated ester 174 was synthesized with excellent enantioselectivity via the Horner-Wadsworth-Emmons reaction (Scheme 66). 84 Scheme 66 Synthetic potential of heterocycles 169…”

“…The resulting adduct 171 undergoes Michael cyclization to intermediate 172, the lactonization of which gives the final product 169. 84,85 Scheme 65 Synthesis of compounds 169 and mechanism their formation To demonstrate the synthetic potential of heterocycles 169, by selective reduction of optically pure compound 169а, chiral aldehyde 173 was obtained, which can be used in further transformations. For example, chiral ,-unsaturated ester 174 was synthesized with excellent enantioselectivity via the Horner-Wadsworth-Emmons reaction (Scheme 66).…”

Synthesis of 5H-Chromeno[2,3-d]pyrimidin-5-one Derivatives via Microwave-Promoted Multicomponent Reaction

“…Chroman-4-one as a privileged motif widely exists in natural products and bioactive molecules. Thus, chroman-4-one-based substrates (e.g., 3-formylchromone) were often used as versatile modules to generate diversified natural product-like scaffolds. − 3-Formylchromone can undergo not only a series of annulation reactions − but also various ring-opening reactions − owing to its structural characteristics. Continuing our ongoing interest in N-heterocycles, − we designed a new MCR including 3-formylchromones, amines, and formaldehyde to construct 1,3-oxazinane-fused chroman-4-ones (path b in Scheme ).…”